Better handling of disabled layers when editing a footprint (value, ref) from the board editor (avoid the "illegal layer" message box when possible).

Previously, only the lib named "power" was used (and therefore power parts defined in other libs not shown).
Now, all power parts can be loaded from any library.
Also, when loading power parts from the chose component dialog or the lib viewer, libs and parts are filtered:  only power parts and libs containing power parts are listed.
Hotkeys: move a few global strings in the files where ther are actually used (and make them local.) and code cleaning.
Fix a few other minor issues.

Removing trailing spaces in some files.

Fix some issues in filling zones normals.
Fix an issue with some models that have materials but didn't defined the diffuse color.
Workaround for Bug #1443431.
Implement some missing "code logic" for pervertexperface normals.
Remove some not used functions.
Calculate normals using double type.

3D viewer: minor fixes. Use our class REPORTER to show warning messages and activity info when building the 3D board view. Add a few comments in sources.
Very minor other fixes.

3D viewer: fix (the fix is not perfect) a minor issue in zone rendering: copper thickness was not good when the option 'Show Holes in Zones" was OFF, and "Show Copper Thickness" ON.
Fix a few coverity minor warnings.

Eeschema: fix a crash on undo command, which sometimes happens after a wire /bus creation command was aborted.
(probably fix  Bug #1434988)

* The SCH_COLLECTOR m_foundItems was being obsoleted after a pin name search.
  If a library edit changed the found pin name, the cache still held the now
  missing library pin and would segfault on next search due to the cache being
  out of date.

board_items_to_polygon_shape_transform.cpp: remove full duplicate code between DRAWSEGMENT and  EDGE_MODULE, and fix incorrect conversion of DRAWSEGMENT polygon type to its polygonal shape.
Gerbview: better info from X2 filefunction attribute displayed in layer manager about copper layers

* Remove redundant definition of KICAD_DATA_PATH since DEFAULT_INSTALL_PATH
  was already defined.
* Use DEFAULT_INSTALL_PATH as the substitution for the default environment
  variable paths.
* Add option to define DEFAULT_INSTALL_PATH during CMake configuration with
  fall back to CMAKE_INSTALL_PREFIX if not not defined.
* Developer note: this change is primarily for package builders where
  CMAKE_INSTALL_PATH is the path where the package builder temporarily
  installs the build output before creating the package.  When building
  packages, DEFAULT_INSTALL_PATH should be set to the path where the
  package will be installed by default.

Pcbnew: always save the line width of footprint graphic edges in files, to allow width = 0 in polygon outlines.
(should not change anything currently for all existing footprints).

Extend max number of units per package: fix incorrect unit string for unit >= 52. Fix unit list limited to 26 in dialof edit compinent in schematic..cpp
lib_pin.cpp: in 4 functions, use an unsigned param instead of int, for  a better code.

Eeschema: extend max number of units per package to 52 and clean code to easily extend this value upto 26x26  (but 52 is a reasonable max value).
Fix a few minor coverity warnings.
Add about_dialog typo fix from Nick Østergaard

Modview: fix issue about mouse on wrong monitor when starting Modview.

* Improve schematic label edit dialog.
* Rename SCH_SCREEN::BuildSchCmpLinksToLibCmp() to SCH_SCREEN::CheckComponentsToPartsLinks()
  for improved readability.

Pcbnew: duplicate and create array: popup menus in legacy mode: remove these options for a few items which cannot be (safely)  duplicated (pads in board editor, and a few others )
Modedit, GAL mode: fix a crash when a duplicated area includes the ref or value fields.
Add missing bitmap for pad enumerate.
fix bad flag for Portuguese language.
Fix a few typo in messages.