Fix bugs in qnet when trying to delete a point in an empty net; deleting all...

Fix bugs in qnet when trying to delete a point in an empty net; deleting all measures in a point;  repititious warnings loading new groundsource files.  Added more gui testing.  Fixes #1491, #1493, #1655.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@5174 41f8697f-d340-4b68-9986-7bafba869bb8