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.

Make dialog footprint wizard list resizable.

(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!

It crashes Adobe's own implementation of postscript!

All: change some texts and messages hard to translate, or not translatable (and some incorrect messages).
Pcbnew, layer manager: add option (popup menu) to always keep copper layers not visible but the active layer, even when the active layer is changed.
Usefull for multilayer ( more than 4 layers) PCBs.

In particular the new mechanism for handling extended color palettes is in place,
included renaming the ini keys and saving the color name instead of its index; this means better forward compatibility with palette changes.

Since ini keys are changed, colors will be reset

Eeschema: Minor changes in dialogs to ensure a better likeness between dialogs on Linux and Windows (mainly, remove some useless wxStaticBoxSizer in dialogs)
Update Clipper version.

Minor changes in dialogs to ensure a better likeness between dialogs on Linux and Windows (mainly, remove some wxStaticBoxSizer in dialogs)

Minor changes in dialogs to ensure a better likeness between dialogs on Linux and Windows (mainly, remove some wxStaticBoxSizer in dialogs)

Implemented the LAYER_NUM typedef (LAYER was already taken as a class name...) to represent a layer number.

(meaning was inverted)

- Renamed ReturnMaskLayer to GetLayerMask (since it's a plain getter)

pcbnew: fix some cosmetic issues mainly on Linux ( these issues could be very dependant on wxWidgets/Gtk versions)

Fix many issues in config functions, mainly a rounding issue when a double is stored in wxConfig file (was stored only using 4 digits in mantissa)
Remove dead or obsolete code.