Points now own and delete their measures. ControlNet now notified of changes...

Points now own and delete their measures.  ControlNet now notified of changes (like adding and removing measures).  Returning pointers to measures is now safe and encouraged.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@1517 41f8697f-d340-4b68-9986-7bafba869bb8