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://f.cl.ly/items/263z0d3M0d0v2O0b462Q/Screen%20Recording%202014-09-11%20at%2004.20%20PM.gif)