Added support for handling versioning patterns in filenames that are made from...

Added support for handling versioning patterns in filenames that are made from dates.  The HighestVersion() method can now get the highest dated file by creating a pattern enclosed in curly braces.  The system will then use Qt's date syntax to find the highest dated file.  Similarly, a new version of a dated pattern will be created, which always creates a file for the current date following the given pattern.  The code in Filename was cleaned up and generalized to support these changes, and new public and private member functions were added as a result.  The unit test was also expanded to test this functionality, and to test picking up a file versioned starting at 0.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@4047 41f8697f-d340-4b68-9986-7bafba869bb8