ENH: enable using the picking manager

Turn on the picking manager on the interactor when creating the first
fiducial, ruler, ROI.
Only for VTK6, solves the issue of picking fiducials in placed order
rather than 3d depth order.
Dragging fiducials near other ones will sometimes cause a jump, but now
the 3d glyph position and the MRML node location stay in synch.

Issue #3319

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23178 3bd1e089-480b-0410-8dfb-8563597acbee