Footprint wizard converts from user units to internal units back and forth, so user can type in mm or mils now

This is *a work in progress*, so some features are missing, and/or could be modified.
Mainly keepout zones are not yet exported to autorouters, and pads are not taken in account.
Some code cleanup in polygon.*

Add copy to text items in pcbnew. Automatically mirror text items added to back silkscreen (bug 1017446).

* Add s-expression file parser object and keyword files.
* Fix minor issues with s-expression file formatting.
* Fix a minor bug the zone container fill state parsing in the legacy plugin.
* Move EDA_TEXT visibility definition to eda_text.h.
* Add minor BOARD_ITEM object improvements to support s-expression file
  parser.

Minor code cleaning in autoroute files.

Eeschema: Fix incorrect display refresh when editing the reference of a component from the popup menu.

3D viewer: fix incorrect scaling factor when using nanometers.
Very minor other fixes

* Footprint wizard C++ generic classes
* Footprint wizard C++ to python wrappers 
* Automatic plugin loader from ~/.kicad/plugins
* Python plugin architecture: Footprint wizards

Fix some comments.  Enhance LEGACY_PLUGIN such that it can tolerate, then fix bad legacy footprint libraries containing duplicate footprint names.
This may have been an undocumented bug from more than a year ago, which manifested itself in *.mod files containing duplicate names.
LEGACY_PLUGIN loads those now quietly, but appends "_v2", "_v3", etc. to each succeeding duplicate sharing the same name.

base on expected text and current window font.

Expand the virtual world to 2.14 meters in the nanometer build of PCBNEW.
This seems to be holding up for now.

Delete LEGACY_PLUGIN cache after deleting library of same name.
Remove automatically generted freerouter help header.
Add Normalize() to BOX2.
Clamp some values in the virtual space of drawframe.cpp

Should allow Pcbnew code easier to change and Gerbview code more understandable and easier to maintain.
Code cleaning (remove dead code, add comments).
Minor other enhancements.

Add patch from Lorenzo Marcantonio. Fix some warning issues, and zlib issue under Windows (zlib sources added)

All: change MILS_TO_IU_SCALING_FACTOR constant to IU_PER_MILS ( and MM_TO_IU_SCALING_FACTOR to IU_PER_MM)
Also fix bug 985654.

All: change MILS_TO_IU_SCALING_FACTOR constant to MILS_PER_IU  ( and  MM_TO_IU_SCALING_FACTOR to MM_PER_IU)
Also fix bug 985654.

Other scaling factors (MILS_TO_IU_SCALING_FACTOR and DECIMILS_TO_IU_SCALING_FACTOR)
also defined only in convert_to_biu.h.
Allows different scaling value for Gerbview.
Needs more tests.

solution to see that it was not pre-computing constants when used in static initializers.

So we have two use cases, and need two solutions to be optimal, since the compiler 
is too stupid to do the right thing.

I think we need something else for compile time computable constants, to be optimal 
in both use cases.  There is quite a bit of code savings by using a macro for that 
situation from my testing.  To fully capitalize on this, we need to go back and make 
Mm2mils() and what not macros also, or have MACRO versions of them too.