Bug 953033 - Add Dzongkha Input Method for B2G

I just added Dzongkha input method for B2G. Dzongkha is national language of Bhutan. This fixes the bug 95033 and also adds support for writing Tibetan (bo-CN) and some other language based on tibetan scripts.

I think the Dzongkha font should be merged before merging this PR. 
That PR is available here - https://github.com/mozilla-b2g/moztt/pull/30

and the bug details is here

https://bugzilla.mozilla.org/show_bug.cgi?id=953033