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.

An ugly if-condition replaced with a CACHE'd cmake variable.

* 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