62 Use MySQL as backing store for users

This is a pretty significant branch that excises MongoDB and replaces it with MySQL (via [Waterline](https://github.com/balderdashy/waterline)). Significant changes include:

- Complete removal of MongoDB
- Replacement of Mongoose user model with a Waterline one
- Update of all methods interacting with the user model to account for the new flat structure of oAuth credentials
- Minor updates to the frontend that make its handling of authentication state less idiotic

This is still in progress and cannot be merged until all items in this ticket are addressed: https://github.com/Fauntleroy/tandem.io/issues/62