Class Pick3DObjectToggle

 object --+    
          |    
_PickToggle --+
              |
             Pick3DObjectToggle

Class meant to replicate a Maestro pick toggle.  This object allows you to
pick objects from the schrodinger.graphics3d module.  This picker allows you
to pick any object assigned to the picking category argument 'pick_category'

Arguments:
checkbox      - The QCheckBox object for the picking toggle
pick_function - Will be called when a bond is picked. Must be a callable
                function that accepts two arguments (atom numbers)
pick_category - The category of objects to pick, this string should match
                whatever value you passed to the 3D Objects when you
                created them.

The following options are supported:
  pick_text     - text that will be displayed in Maestro's status area
                  (default "Pick a bond")