Refactor Mongoose code with Bluebird

[Awk34]

Right now we're doing require('bluebird').promisifyAll(require('mongoose')), but Mongoose 4 supports promises now. We should instead do this:

import mongoose from 'mongoose';
mongoose.Promise = require('blubird');

This would remove the need for methods like findAsync, and instead we would just use find. This requires a lot of refactoring.