ENH: Add qMRMLTreeView::setSortFilterProxyModel function to be able to set custom proxy models to the tree view

Signed-off-by: Jean-Christophe Fillion-Robin <jchris.fillionr@kitware.com>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@21633 3bd1e089-480b-0410-8dfb-8563597acbee