More button action changes.

* Removed toggle display/mode features as they are no longer supported by xsetwacom.
* Unified button action selections accross the pen widget and pad widget tabs.
* The mouse button selection dialog now sets the current setting as default.
* Added a group box to the mouse button selection dialog to make it look nicer.
* Named the default mouse buttons which should be available on all mice.
* Removed obsolete toggle code from ButtonShortcut.
* Updated ButtonShortcut unit test to reflect the changes.