BUG: Disable fiducials in light box mode. See 0001690

Fiducials are not being properly positioned when in light box mode, this
change disables them and gives the user a warning that they are being
disabled (new fiducials can still be placed, but will not be visible until
you exit light box mode).

This change fixes bugs that were left from the attempt to use the point
handle widgets in 2D so that they can be properly hidden: fix the
visibility setting on the point handles in light box mode, disable
the point handles when invisible so that they don't become visible
when the mouse is near it, updated a visibility check comparision
to match return type from method.

Also removed warning messages by casting the 3d handles before changing
the picking state.

Fixed a bug wherein if you had a mix of fiducials having been placed
in lightbox and not light box mode, the seed widget would have a mix
of 2d and 3d handles.

This fix removes all the current handles so that they're properly
recreated as the necessary type.

Issue 0001690

From: Nicole Aucoin <nicole@bwh.harvard.edu>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@24726 3bd1e089-480b-0410-8dfb-8563597acbee