Migrate to Cedar stack (#39)

The name of the new app is **seattlerb-cedar-phiggins**

For testing:

- [x] Merge master into this branch. (@phiggins)
- [x] [Reprovision Addons](https://devcenter.heroku.com/articles/cedar-migration#reprovision-add-ons)
- [x] [Copy Configuration Variables](https://devcenter.heroku.com/articles/cedar-migration#copy-configuration-variables)
- [x] [Memcache](https://devcenter.heroku.com/articles/cedar-migration#memcache) ? (I assume we're not using memcache)
- [x] [Migrate the data](https://devcenter.heroku.com/articles/cedar-migration#make-cedar-app-live-postgres)

To make the switch:

- [ ] [Turn on maintenance mode](https://devcenter.heroku.com/articles/cedar-migration#make-cedar-app-live)
- [ ]  [Migrate the data (again)](https://devcenter.heroku.com/articles/cedar-migration#make-cedar-app-live-postgres)
- [x] [Transfer custom domains](https://devcenter.heroku.com/articles/cedar-migration#custom-domains)
- [ ] [Transfer DNS (can we just rename the apps?)](https://devcenter.heroku.com/articles/cedar-migration#dns)
- [ ] [Turn off maintenance mode](https://devcenter.heroku.com/articles/cedar-migration#turn-off-maintenance-mode)