Adds longerusername to support usernames longer than 30 characters

External auth providers often have usernames longer than 30
characters, and adding this django app extends that to 255 with a
patch and schema migration.  This change should not affect the
username length limitations for internal user accounts.

I was wondering if @jbau had come across this yet as it just bit us
with CAS usernames much longer than 30 characters. This is mostly
an ops change and DB migration, so maybe @e0d or @jarvis might
want to take a look.

I also would understand if due to the somewhat hacky nature of
longerusername that you guys may not want this, and I'm open
to other suggestions.