Add Wasta 14 keyboard handling via IBus alone

Produces a list of available keyboards properly, but doesn't attempt
to switch keyboards.  The code is adapted from the combined keyboard
handling written to support Trusty.  It's too bad the two systems went
their separate ways in this area.
I would guess the function turns into a no-op for some number of versions before being removed altogether, at which point the program wouldn't compile.  And Precise (which we still support) uses version 2.32, so it's still needed there.