Address facebook username conflict

[klnusbaum]

It is possible that when authenicating via facebook, a username may conflict with a username we already have in the database. We need to find a way to address this.

[klnusbaum]

Idea: append numbers to the facebook username. Since we never use the literal user name for queries, if there is a duplicate, say "steve", we can just store it in our database as "steve1". if there's already a "steve1", then use "steve2", and so on and so forth.