Error logging

[zkwsk]

I don't think this is high priority, but it would be nice to have error logging set up so we're ready the day we decide to go properly live with one of our applications. Further, it is good for the students to see how it can be set up and used for debugging.

The goal should at the very least be to log all serverside errors to a file that can be reviewed from the heroku interface (probably with the Papertrail add-on).

Could be interesting to make an access log as well, but that's even less of a priority.