* Support link and group objects
* Support view sync by implementing view provider API getMDIView()
* Use handleChangedPropertyType() for object migration instead of
reimplementing Restore() because of a lots of changes in
PropertyContainer::Restore().
* Various other small fixes.
- use current 3D window direction as starting
direction for DrawViewPart and ProjectionGroup
- if a Face is selected, use Face normal as
starting direction.
