Added new support classes for targets and shapes for Cassini Rings. ...

Added new support classes for targets and shapes for Cassini Rings.  References #775 and resolves #1114.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@4780 41f8697f-d340-4b68-9986-7bafba869bb8