* 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  out of date.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.

eeschema: fix Bug #1437604 (double translation of some messages in pin editor dialog) relative to some static strings flagged "to be translated".
This is due to the fact static strings flagged translated ( _("string") notation)  are not translated  when they are static only if they are not inside a dll.
When they are static inside a dll, the dictionary is already loaded, and the constructor translate them.
Therefore they can be translated twice in dialogs are calling wxGetTranslation to show them, if the application is run from kicad.
But if the application is run as stand alone, the translation is made only once (as expected).

Fix minor 3D viewer issues (includling change number of segments and its optimization to draw pad holes.)
Fix Bug #1439132 (track and via list on toolbar not always refresh after loading a board).
Remove useless tool in Modedit.

* Fix bug (and Coverity error) when deleting environment variable map entries.
* Remove debug logging code inadvertently left over from development.

3d viewer: fix a few warning coverity (and a potential bug). fp libs wizard: make it internationalized, and replace an untranslatable string created by grouping 3 strings by one translatable string.

Minor fixes: make a message translatable in CvPcb. Dialog choose component: fix a missing min size calculation and make min size bigger.

* Create new dialog to edit environment variables.
* Add helper class ENV_VAR_ITEM to manage environment variable values and
  if they were defined externally.
* A path configuration dialog access to KiCad, CvPcb, Pcbnew, and Footprint Editor
  window menus.
* Add validator for environment variables.