Continued the refactoring process for the various 'equalizer' applications...

Continued the refactoring process for the various 'equalizer' applications referenced in issue #108.  Made 'hiequal' into a class called 'HiEqualization' deriving from 'Equalization'.  The amount of code in 'HiEqualization' has thus been cut to the bare essentials through polymorphism.  However, the application 'hiequal' still duplicates much of the same UI setup code from 'equalizer', thus another abstraction still needs to be made to address this problem.  In the process, a factory class can be designed to construct different 'Equalization' modes.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@2727 41f8697f-d340-4b68-9986-7bafba869bb8