Resolve Authentication Issues

This PR makes some major changes to the way authentication and sessions are managed by the application. In general, the goal was to simplify the codebase to work exclusively with Github authentication and reduce dependencies. This was acomplished by removing boilerplate, moving to client-side session storage, and eliminating the need for a backing datastore.

#### Revisions
- Reduce the number of unused dependencies both within package.json and `require`-ed in the app itself
- Remove the need for a backing database (Mongo) by eliminating the need for a session store (using [client-sessions](https://github.com/mozilla/node-client-sessions)) and eliminating the storage of user accounts
- Migrate from [passport](http://passportjs.org/) to [github-oauth](https://github.com/maxogden/github-oauth)
- Add AirBNB style check via [JSCS](https://github.com/jscs-dev/node-jscs) as per the [engineering handbook](https://github.com/MozillaFoundation/MoFo-Engineering-Handbook/issues/13)
- Add script for `npm test` that includes style and basic route checks

#### Resolves
```
GH-156
GH-149
```

![](http://media.giphy.com/media/I7kkegrRyNrk4/giphy.gif)