BUG: #2983 and #2206 fix position of the dicom popup

Detect when the window is already open so it doesn't get repositioned
more than once.  Also keep track of when you have applied the
settings geometry and then don't apply the standard placement
in that case.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@21782 3bd1e089-480b-0410-8dfb-8563597acbee