Can't login as admin when email addr is not set
I noticed that we didn't set the admin SSO user's email_adr properly (I fixed this in openappstack!413 (af0ec7bf)). Using the right credentials, the admin couldn't login, and it was unclear why (the UI only showed sth like 'cannot login').
So either we let users login who don't have an email adr set (and nudge them to add one), or we show a proper error message that login failed because of a lacking email addr.
Related to #36 ?
This also showed the importance of testing SSO in CI, which openappstack!413 will cover.