Restrict allowed username

[Ryan J Ollos]

This ticket captures some discussion among otaku42, rjollos and hasienda regarding problems with certain usernames on t-h.o. Specifically, dev and one were pointed out to be problematic.

Some solutions were proposed:

1. Prevent some common words from being used as usernames (e.g. admin).
2. Minimum length for usernames.

It was also suggested that we might increase the min length for auto-wikification.

Some thought should also be given to how we will deal with improper usernames that we don't think of beforehand and preemptively blacklist. If we can confirm that they are really spam, then we just delete the accounts, but if they are not spam, perhaps we can just immediately contact the user and help them to change their username.