Created AbstractMultipleChoiceFilter to support filters needing combo boxes...

Created AbstractMultipleChoiceFilter to support filters needing combo boxes (usually attributes of enumerated types).  Added whatsthis action to toolbar and menu.  Added whatsthis descriptions to enableSortAct and freezeTablesAct.  Added 'BETA VERSION' to window title.  Improved action passing between CnetEditorWidget and CnetEditorWindow.  Added an icon for freezing tables.  Improved how actions are handled in toolbars and menus.  Created new filter for point type using functionality provided by the new AbstractMultipleChoiceFilter.  Added minimal support for keyboard control of the tables.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@3408 41f8697f-d340-4b68-9986-7bafba869bb8