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
Merge pull request #18 from TeaWithStrangers/cityDeleteAPI

Add `DELETE` route for an Individual City
Merge branch 'master' into getandputcities

Update getandput branch to match changes from #17 that are now in master.
Should be good to go for implementing updates.

Conflicts:
	lib/server.js