Fem: [skip ci] set backend of matplotlib to Qt5Agg

Version 0.19

App/Gui: New restoreError Document status and Gui pop-up

========================================================

If the restore of Document.xml results in invalid Document.xml (because unhandled exceptions occurred), the
document status Document::restoreError is set. The GUI or Mod/Web if a link was clicked, show a pop-up indicating
this situation.

This commit also shows an appropriate pop-up for the partialRestore when opening from the menu, that before only
appeared when opening by clicking a link.

Fixed typo in last commit

pre-select name filter in import/export file dialog

AddonManager: Skip non-github addons

replace insecure use of eval() with proper use of units

FEM: ccx tools, set back the assignment of linux and osx ccx binary path

Fixes Bug 2034. Made Part dimensional arrows proportional to line len…

…gth and radius

fixes FreeCAD#3421: Duplicate workbench message