Add users_seen to Group
Always tag user email addresses
Remove sentry_user_emails from apps
Send regression_signal using send_robust
is_authenticated is no longer required, and email is suggested
Ensure user_email is automatically tagged (tests)
Fire buffer_incr_complete signal and bind it to updates on the users_seen column
Import ordering
Remove dupe signal
Actually record users_seen correctly
Correct users_seen behavior and add tests
extra is unused
Merge branch 'user-tracking'