Extract reused Warden key constant
Warden hook: refactor to not perform inline assignment for clarity
Warden.after_set_user called regardless of signin method

The combined effect of this commit is a 2FA code will be sent out once automatically when a session starts.
Merge pull request #2 from checkdin/bugfix/two-factor-after-password-reset-0.2

Bugfix/two factor after password reset 0.2