BUG: respect don't show again on fiducials conversion

Define a new button with an AcceptRole to have it saved
in the config file, following the pattern of the Delete
pop up boxes.

Issue #3663



git-svn-id: http://svn.slicer.org/Slicer4/trunk@23525 3bd1e089-480b-0410-8dfb-8563597acbee