ENH: Implement feature 2885, display ruler projection on 2D viewers.

Add options to display the projection of a ruler on the 2D slices.

Code from Laurent Chauvin 
https://github.com/lchauvin/Slicer/commit/203b44301c0421d619d68e2ccd3a13dee0047cf0

Issue #2885


git-svn-id: http://svn.slicer.org/Slicer4/trunk@21649 3bd1e089-480b-0410-8dfb-8563597acbee