BUG: add missing StartPlaceMode method

Laurent's extension was using the Annotation module logic
StartPlaceMode call and it wasn't working. Added it to
Markups logic and debugged it to work to set the mouse
mode to place Markup fiducials. Added a return boolean
to check success. Updated testing.



git-svn-id: http://svn.slicer.org/Slicer4/trunk@22431 3bd1e089-480b-0410-8dfb-8563597acbee