New feature: Edit Sketch datum constraints from data Property view

This feature shows in the data properties associated to a TreeView element,
the datum constraints, i.e. those with an associated value.
+ fix build failure on Windows, remove unused headers, whitespace improvements
Fix bug 1643: Projections are always added to the first drawing page
Fix typo.
1659: 3dconnexion space navigator moves view even when FreeCAD is not the active application

Check whether the freecad window is active before relaying the space navigator events.
OCCError derived from RuntimeError
define Base::BaseExceoptionFreeCADError
inherit Part.OCCError from Base.FreeCADError
Add Part/AppPart.h with PY_CATCH_OCC macro