Bb 53 2

Fairly big changes:

* Middleware added in BlueBottle (requirements.txt has been updated, the feature branch is pushed: new tag will be needed)
* Middleware needed for locale awareness in the API: tweet texts are built inside the model and need to be translatable
* Projects, tasks: facebook og:tags are okay, correct image is provided. Tweets: specified text is built in the model
* Settings added: twitter handle per locale, with a default falling back to the dutch handle (say, a third language gets added and no extra account is created on twitter etc...). Also partly the cause of the extra middleware required.

TODO: rest of the meta doc on Facebook/twitter