TDD + BBD = <3

Added:
* Intial tests for below using [mocha](http://mochajs.org) w/ [chai](http://chaijs.com), and [supertest](https://github.com/tj/supertest)
  * `/api/users` - for both guests and standard users
  * `/api/users/{id}` - for standard users
  * `/healthcheck` - server status route
* Simple test data for User model
* Some [Continuous Integration](http://wikipedia.org/wiki/Continuous_integration) support using [TravisCI](https://travis-ci.org)

Changed:
* Removed some overly restrictive validation rules from User model.
* `grunt test` now runs the full set of tests, while `grunt watch` only runs syntax checks (with respect to testing)