Pcbnew: fix minor bug about  plot line width.

* Fix a bug when full file name and path are passed to FOOTPRINT_INFO::
  ReadFootprintFiles() which I created in bug fix lp:593989.
* Fix a wxString debug assertion in EDA_APP::InitEDA_Appl() when the KICAD
  environment variable is defined as an empty string.
* Add error dialog when libraries cannot be found in system search path
  when loading footprint using the select footprint dialog.
* Add footprint library name column to the EDA_LIST_DIALOG when selecting
  footprints from the list.
* Allow reading all columns from the selected row in EDA_LIST_DIALOG.
* Remove redundant sort from EDA_LIST_DIALOG constructor
* Add library name member variable and accessors to FOOTPRINT_INFO.
* Make headers translatable for Eeschema select component from list dialog.
* Add some helper methods to FPID for identifying the FPID type and validity.
* Remove a bunch of trailing whitespace and add missing license comments.

Eechema: fix bug : when saving the schematic project, the lib cache was saved under the current sheet opened, not the root sheet.
Pcbnew: clamp default plot line width between 0.02 and 2 mm. the other bug (saving this parameter in internal units instead of mm is not fixed)

(explanation: float is implicitly promoted to double anyway, it's only useful
for storage; also a fp variable forces conversion of other int in the expression
without needing a cast)
Typo fixes in some comments 'floatting' -> 'floating' :D

Mass parameters in gerbers can't use scientific notation (altough some software 
allow it), so the %g format was not correct.

The plan goes like this:
- eeschema still uses int in decidegrees
- all the other things internally use double in decidegrees (or radians
  in temporaries)
- in pcbnew UI the unit is *still* int in decidegrees

The idea is to have better precision everywhere while keeping the user with int i
angles. Hopefully, if a fractional angle doesn't come in from the outside, everything
should *look* like an integer angle (unless I forgot something and it broke)

When the time comes, simply updating the UI for allowing doubles from the user should
be enough to get arbitrary angles in pcbnew.

This is a starting point of some code enhancements relative to polygons in Pcbew and 3D viewer.

New conversion routines and sin/cos implementation for angles in decidegrees

* All items shapes  are converted to polygons.
* Polygons are merged layer by layer (for calculation time reasons,zones are not merged)
* for copper layers, vias and pads holes are substracted from polygons (but, for calculation time reasons,  not inside zones areas).
* the look is better, mainly when displaying the copper thickness
* solder and paste layers are now shown in 3D viewer.
* the code was seriously cleaned (but still needs to be enhanced).
* Note this is a work in progress which needs refinements.

- Removed spurious int casts (these are truncated anyway and will break
  doubles)

- Applied the Distance, GetLineLength, EuclideanNorm, DEG2RAD, RAD2DEG
  ArcTangente and NORMALIZE* functions where possible

- ArcTangente now returns double and handles the 0,0 case like atan2, so
  it's no longer necessary to check for it before calling

- Small functions in trigo moved as inline

In most case the assignment to null was not necessary since it was easily provable that the (local) variable wouldn't have referenced after that anyway.

* Tweak the NETLIST_READER code to allow for component footprint names that
  are not found in any library to generate a warning instead of an error and
  update the board accordingly.
* Don't display undo warning in netlist dialog when dry run option selected.
* Rename netlist_reader_common.cpp to netlist_reader.cpp
* Rename netlist_reader_firstformat.cpp to legacy_netlist_reader.cpp
* Rename netlist_reader_kicad.cpp to kicad_netlist_reader.cpp
* Remove cvpcb/read_write_cmpfile.cpp and move the single function it
  contained into cvframe.cpp
* Remove cvpcb/loadcmp.cpp and move the single function it contained into
  class_DisplayFootprintsFrame.cpp.
* Remove cvpcb/readschematicnetlist.cpp and move the single function it
  contained into cvframe.cpp.
* Remove cvpcb/setvisu.cpp and move the few functions it contained into
  the appropriate source file.

* Create separate NETLIST object to hold contents of netlist files.
* Read entire netlist and footprint link files before making applying
  changes to board.
* Add BOARD::ReplaceNetlist() function to eliminate the calls between the
  NETLIST_READER, PCB_EDIT_FRAME, and BOARD objects.
* Change placement of new components below the center of the current board
  or in the center of the page if the BOARD is empty.
* Add dry run option to netlist dialog to print changes to message control
  without making changes.
* Add button to netlist dialog to allow saving contents of message control
  to a file.
* Eliminate the need to compile netlist_reader_*.cpp in both CvPcb and Pcbnew.
* Add netlist_reader_*.cpp to the pcbcommon library.
* Remove redundant load component link file code from CvPcb.
* Modify CvPcb new to work with the new NETLIST_READER object.
* Add compare() function and < and == operators to FPID object.
* Add REPORTER class to hide an underlying string writing implementation for
  use in low level objects.  Thank you Dick for the idea.
* Lots of minor coding policy, Doxygen comment, and missing license fixes.

Also removed EDA_DRAW_FRAME::OnGrid which was totally dead (empty and unused)

Pcbnew: load footprint from modview: Because modview allows user to choose the footprint library, the selected library is forced when the footprint is loaded.
I am not sure this is 100% better, but this new behavior has some advantages, mainly in the footprint editor (you can load a footprint outside the selected library)

Slightly retuned for compensating the new position.

Dynamic contrast for netname and pin numbers ('halo' text)
Handle netname drawing even on diagonal tracks

More layer classification cleanup

bit string version of property_tree. The ram resident structure of the ptree is
mostly compatible with one created using the xml_parser from
boost::property_tree, with slight differences in the way atoms are stored. The
result is you can use Format() to convert from xml to s-expression, but not the
other way around. You can write a simple s-expression beautifier in just a few
lines of code.

The main value however is the s-expression parser, i.e. Scan(), which is an
alternative to crafting a custom recursive descent parser for a particular
grammar. The tipping point depends on whether you want to read only a small
portion of a much larger document. If so, then using the ptree will likely be a
"faster to code" route. Documentation on how to navigate a ptree can be found on
the boost website and there are a number of examples in the
pcbnew/eagle_plugin.cpp file in this project. Powerful path navigation support
makes it easy to extract a subset of a ptree.

(when disabled they are shown as standard holes, a lot less distracting
than the previous fixed yellow color)

Better description for entities on right click menu and panel
Typo fixes and some comment reformats

Charras beat me on fixing the include/sch_item_struct.h include issue from 4069

Gerbview, layer manager: add option (popup menu) to always keep layers not visible but the active layer, even when the active layer is changed.
Pcbnew: fix swig warning for operator EDA_COLOR_T::++  (changed to function EDA_COLOR_T:: NextColor)

the spurious warning about stuff that couldn't be seen when changing
colours.
NOTE that the 'net name' layer is present and configurable but non used 
anywhere!