Fix: change random usernames to "user[0-9]+"

People joining a room without a Username gets one picked at random. This is a bit confusing, since the said usernames do not look like they were picked at random. Using something like "User[0-9]*" would be clearer in my opinion.

Credit: Francois Fleuret

-- Yeah, that would be clearer. I chose to go with the first names of different scientists, but perhaps it is creating more confusion. Maybe a compromise would be to have a box asking for a username when the site first loads. -Juan