ENH: put more checks into fiber editing

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22069 3bd1e089-480b-0410-8dfb-8563597acbee
ENH: moved Enable Tracks button to the top

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22070 3bd1e089-480b-0410-8dfb-8563597acbee