EXP-1533 FIX -- As a FUI user, I'd like to be able to remove toolbar buttons...

EXP-1533 FIX -- As a FUI user, I'd like to be able to remove toolbar buttons without having to drag them anywhere

* Added "Remove this button" option to the toolbar context menu
* Added code to track the right mouse click and execute the action to remove the
  appropriate button on the toolbar.

Reviewed by surly leyla