Bug 821646 - [Settings] Pin the language associated keyboard at the top of the keyboards list. r=arthurcc

Make the keyboard associated with the current language always enabled by pinning
it at the top of the Keyboard Layouts list. If the current language doesn't have
a keyboard layout in the list from settings, the English keyboard is pinned.
Merge pull request #9032 from mcirlanaru/bug_821646

Bug 821646 - [Keyboard] Don't allow 0 selected keyboard layouts, r=@crh0716