Moved checks into separate group in GUI. Made new optional check CONVEXHULL,...

Moved checks into separate group in GUI.  Made new optional check CONVEXHULL, making convex hull check no longer performed no matter what.  Results of CONVEXHULL check now go to file [PREFIX]ConvexHull.txt, containing a cube name and serial number row for each failure.  Improved documentation for CONVEXHULL check to better explain the concept and how to pick a good TOLERANCE.  These changes reference issue #245.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@3023 41f8697f-d340-4b68-9986-7bafba869bb8