Article size and count limits

Limited the number of articles, and the size of article bodies. This, together with the reCAPTCHA setup from Email verification and reCAPTCHA signup protection should prevent the most basic types of denial-of-service attacks by filling up our database.

The limits can be increased by admin users from the web UI, and will be done generously when it is evident that it is not a DoS attack. Admin users are also a recently added feature.