Minor doc update.

Apply patch from Cirilo Bernardo with some minor changes: mainly allows also the solder mask layer and keep ref and value fields on the silk layer.

* Fix assertions in Eeschema when editing net labels, electronic rules check,
  and plotting.
* Fix assertion when opening PCB calculator.
* Fix assertions in Pcbnew when changing footprints in footprint properties
  dialog and adding or editing text.

Polyline.h: remove useless class CRect. Use the more powerful EDA_RECT instead. Clean and remove duplicate code.

* Patch was taken from https://trac.macports.org/ticket/44524 for the upstream
  bug of http://trac.wxwidgets.org/ticket/16329.

Fix many doxygen warnings (due to missing info, old comments, typo ...) when building the doxygen doc.

Add check for correct wxGTK version report by wx-config. If incorrect cmake fails. Compare https://bugzilla.redhat.com/show_bug.cgi?id=1077718

Fix CMake warning caused by removal of boost dependency when not actually building boost from source.

* Move all Windows install subfolders from ${CMAKE_INSTALL_PREFIX}/share/ to
  ${CMAKE_INSTALL_PREFIX}/share/kicad/.
* Remove unused define DEFAULT_FP_LIB_PATH from build configuration.
* Remove Boost target when skipping internal Boost build.
* Update INSTALL.txt to reflect install tree changes.

Fix minor issues about translated strings and coding style. Add comment relative to file function info  in X1 gerber file format.

Pcbnew: Console python: use a wxMiniFrame to show the console and remove the management by a EDA_PANEINFO, which was not the right way to manage this console.

Pcbnew: Console python: use a wxMiniFrame to show the console and remove the management by a EDA_PANEINFO, which was not the right way to manage this console.

Pcbnew: fix a serious bug in ZONE_CONTAINER class copy constructor: a pointer was not initialized. Pcbnew crashes when deleting or filling a copied zone.
Eeschema: remove dead code and uncrutify class_netlist_object.h

* Add more missing source code licenses.
* Fix coding policy violations (tabs and trailing white space) in Python
  scripting code.
* Add stable release policy to full documentation build.

Kicad manager, Gerbview: When running Gerbview from Kicad manger, set the Gerbview  CWD to the current project directory.
Therefore, when trying to open Gerber files, the default directory is now thecurrent project directory.
(fix Bug #1380088 )