Graphing code integrated into this class. This class now acts as a node or...

Graphing code integrated into this class.  This class now acts as a node or vertex class for graphs where edges are connections between images

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@1821 41f8697f-d340-4b68-9986-7bafba869bb8