[#30] Auto-login upon registration
  - students and teachers get auto-logged in on registration
  - removed clear text password form welcome email
  - modified welcome email text to reflect the fact that login has happened
  - (unrelated) suppressed devise warning message due to deprecated config
Merge remote-tracking branch 'heroku/master'
Merge pull request #32 from adamarla/master

Auto-login on reg fixed Issue #32