ENH: #2543 small changes to documentation for FiberBundleToLabelMap

Clean up the documentation and improve the display of the name.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22147 3bd1e089-480b-0410-8dfb-8563597acbee
BUG: #2948 save updated MRB file name for next save step

The URL instance variable of the scene is used to store
the source / destination of the scene, so it needs to be
set for use as the default for the next save operation.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22148 3bd1e089-480b-0410-8dfb-8563597acbee