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.

3D-viewer: Fixes and enhancements (add 3D bounding box for components). Add comments in header files. Fix some coding style issues.

* Make OK button the default action in the 3D viewer option dialog per UI
  policy.
* Fix standard button sizer padding in 3D viewer options dialog.
* Let sizers do their job by using default size for 3D viewer options
  dialog.
* Set 3D viewer hot key to Alt+3 in all parent windows where 3D viewer is
  accessible.
* Minor code cleaning and coding policy fixes.

Minor fix: Gerber X2 attribute: remove one attribute (TF .GerberVersion, now no more in use) I added in my recent changes relative to the new J5 gerber version attributes.

Better error messge when a .kiface file ( or,  if it exists, a .dll or .so shared library ) is not found at start up