Modularise controllers folder & add City

* Create controllers folder+index
* Move cityAPI into controllers/cities.js
* Make all responses from server default to JSON with addition of new response
  filter
Add models to the `req` object

As originally exported from the DB object, models were under their own
properties, e.g. 'City', 'TeaTime', etc.  This moves them onto the `models`
property.
Merge pull request #17 from TeaWithStrangers/teatime-basics

City API with Creation and Retrieval of all City objects
Implement City delete; Merge cityDeleteAPI, master

Implements deletion of Cities, updated to reflect changes to code structure made
in master branch afer merging #17.

Conflicts:
	lib/cityAPI.js
	lib/server.js