Fixing shortcut system:
- Take shortcuts automatically from CommandManager.
- Fixed two shortcuts in CommandConstraints (Point on Object - O and
Parallel Constraint - P to SHIFT+O and SHIFT+P to avoid collision with other constraints)
- Fixed shortcuts in CommandConstraintAccel to non-already-existing combinations
- Fixed Sketcher Menu to show accelerators
- Fixed Length Constraint accelerator (D) to SHIFT+D to avoid colision with other higher level FreeCAD accelerator assignment.
- Selection Accelerators now toggle on shortcut execution, and act when no other element is selected (fixed bug)

TODO: Art+Toolbar