Add language

This pull request introduces a dropdown menu for specifying a language either when creating a new compendium, or when adding a new language version to an exisiting compendium. This means that the old way of guessing the language via __detectlanguage.com__ is gone _(bye bye, magic)_.

The listing of available languages when browsing or editing an article is also updated. It is now a dropdown menu, instead of the old not-so-scalable "show all the buttons next to each other" solution. It also features a button for adding a new language version.

![screen shot 2013-06-20 at 00 13 59](https://f.cloud.github.com/assets/1413267/678191/be143094-d92d-11e2-8f70-89859c40c8d8.png)

![screen shot 2013-06-20 at 00 18 42](https://f.cloud.github.com/assets/1413267/678207/3e386e2a-d92e-11e2-90ba-5a580b6631be.png)

closes #58 
closes #57 
closes #55