Prayer letters OAuth2 upgrade

This uses OAuth2 to connect authorize future PrayerLetters.com integrations instead of OAuth1. It also uses OAuth2 for the API requests (with OAuth1 as a fallback for users who haven't been migrated yet) and runs a background job to migrate the old accounts to OAuth2.

I also added code to log the first request exception that then causes a JSON parse exception for the error code in `PrayerLettersAccount.create_contact`. That will hopefully help in tracking the underlying cause of that error in Errbit.

This isn't ready for deployment yet as the `omniauth-prayer-letters` gem it uses is being hosted in my personal github repo, and we need the client id and secrets from PrayerLetters before I can test it out on stage or deploy it to production, but the code is pretty much ready at this point.
I had some trouble with code in models not reloading when I was using guard/spork (only an actual ActiveRecord::Model not just a regular class) and someone online suggested this, and now the reloading seems to work. I'm not 100% this line was what did it (maybe I just needed to restart something). I'll take it out for now and later on if I come to the problem again and that line definitely fixes it I'll more confidently suggest that as a change.