Lobby needs to limit new gitlab name to something like A-Z, a-z, and 0-9

When people attempt usernames with surprising characters in them, gitlab-lobby fails to make the gitlab account. If this is a gitlab-lobby bug, we should fix it and be happy. If this is a gitlab limitation (e.g. "you can't have chinese account names"), we should hack around it in gitlab-lobby by enforcing some rules on names. Otherwise we have people attempting to make accounts which we know will fail.

Thanks!