Add support for updating languages. Closes #187.

Languages can now be added and removed inline thanks to the awesome
Select2 library. The list of accepted languages can be customized in
settings.yml.

Demo:
![Editing languages in Ohana API
Admin](http://cl.ly/image/46132V282d1o/Screen%20Recording%202014-09-11%2
0at%2004.20%20PM.gif)
Merge pull request #231 from codeforamerica/187-admin-languages

Add support for updating languages. Closes #187.