Export user's data

[kubili]

We should support exporting all data we have on/of/by the user. After a request is made, a Celery background task can collect all data (also uploaded photos and everything else) into archive and send a notification e-mail. Before download, we should again check that user has right to download this data (again request password or authentication). So this data is really privacy sensitive so we should be very careful that nobody else can download/export user's data.

[mitar]

Authentication has moved to separate package, so this should be implemented there: mitar/django-mongo-auth#1

In an extensible way so that users of the package can add their own information what should be exported.