BUG: Fixed max allowed module widget size for HiDPI screens

The fixed 500px maximum width for widget minimum size hint is not applicable for HiDPI screens, where 500px corresponds to about 15% or less of the screen width.
Allow widget size to be max(500px, 30% of screen width).

From: Andras Lasso <lasso@queensu.ca>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@25287 3bd1e089-480b-0410-8dfb-8563597acbee