Add Wasta 14 keyboard handling via IBus alone

When IBus is used in Wasta 14, it becomes the sole keyboard handler.
(Wasta 14 is based on Mint 17 using Cinnamon.)
The IBus settings list both XKB and IBus keyboards together, and the
IBus code  handles switching keyboards the same way for both.  Too bad
it's a different approach than Ubuntu took with Saucy/Trusty.