Handle property grid reset case.

Property grid will send null when you reset a value.
Fixed smart manipulator bug

Wasn't calling base class to end manipulation in the case where there
was not manipulation amount. This was causing the tool's handles to not
update correctly when the entity changed.
Duplicate objects - Control + d

Duplicate the current selection via Control + D. Uses the clipboard cut
/ paste system since we need to preserve the entire hierarchy of objects
under a given object.
Clipboard data bug

Min objects in clipboard needs to be 0 for case where we attempt to copy
objects that can't be copied (spline point)
Hide property grid description
Adding size snap to snap state.
User prop grid for snap settings

To make life easier, should make a single property grid that handles
everything?
First pass size snapping.