Change 'Configure Columns' menu entry to be a simple push-button (as apposed to a radio with a check)

MenuAction and supporting/surrounding classes are meant to handle menus with mutually-exclusive menu items (like a group of radio buttons). I'm cheating here by using that API to expose a configure columns menu action, which has no state (at least as far as the menu is concerned)
do nothing if configure columns dialog is canceled
improve UI/presentation for configure columns menu and dialog
pre-populate configure columns dialog with current column state
cleanup code