Added SimpleClans availability within Domain. You can now use:

/domain clan allow <clan tag> to allow a clan to the field.
/domain clan disallow <clan tag> to disallow a clan from the field

SimpleClans is a soft dependency, so it is NOT required for Domain to run, but adds the additional clan functionality if it is available.

Additional Changes:
Removed unnecessary player alerts when selecting items in the GUI
Removed Gray Stained Glass Pane from GUI