Email authentication

Added email authentication to the application. Interviewee and Interviewer emails are specified on the first page and then stored in Redis per interview for authentication on interview startup.
Just verified that if the interview ID doesn't exist in redis, then it will return None for the interview_id and therefore None for the emails as well. The behaviour for this in our case is that the login dialog never goes away and will always say "Invalid email", which I think is the expected behavioud