Bug 936581 - [B2G] Keyboard language display change not visibly apparent
to user.
 - Show a language-specific label (shortLabel) on the IME switching key.
Merge pull request #19428 from RudyLu/keyboard/Bug936581_IME_switch_indicator

Bug 936581 - [B2G] Keyboard language display change not visibly apparent
r=timdream.