+ add class ViewProviderPrimitive to avoid to re-implement setEdit/unsetEdit methods for each sub-class separately
+ avoid using global variables
+ when editing a feature directly pass it to the dialogs
+ when editing a feature then do not use active document as this could point to the wrong object
+ fix undo/redo message
+ re-add '3D View' button to location dialog
The path to the icons is added to `AppPartGui.cpp`
using `Gui::BitmapFactory().addPath()`, so the icons are found
automatically in their new directories.
