BUG: fix tooltips on editor effect buttons

Turns out that even though you can set the tooltip of
a QToolButton it gets overridden by the tooltip associated
with the QAction. So we set the QAction's tooltip
instead.

Thanks to Csaba for pointing out that the tooltips were broken.

From: Steve Pieper <pieper@bwh.harvard.edu>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@24225 3bd1e089-480b-0410-8dfb-8563597acbee