ENH: Added delegate temporarily for qMRMLTableView

Will be removed in next commit. Created to enable special editing of vtkMRMLTableNode cells in qMRMLTableView. This will be useful later for color editing, or if a better solution will be found for checkboxes. This delegate shows a checkbox in the center of the table cell (by default it is on the left), but only allows editing after double click. Thus this will be replaced by simple Qt mechanism with the checkbox on the left.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@24969 3bd1e089-480b-0410-8dfb-8563597acbee