Add option to configure proxy url for testing
Improving RestContext

* Add thePropertyContains() step, used to check for tags.
* Use base_url from Guzzle
* Add support for setting query strings in tests
* Improve error message for property equals
Better handling of JSON errors in tests
Fix post_datetime SQL Create statement - only create if not exists
DELETE /posts/:id - return the post that was deleted
PUT /posts/:id - implementing post updates
Adding further tests and improve some existing ones

* Test for 404 on DELETE missing resources
* Test for 404 when try to GET non existent resource
* Test for being saved tags in posts
* Test for searching posts
  * Add extra fixtures to support this
* Test for 404 on PUT/updating a non-existent resource
Make GET/PUT/DELETE on missing resources respond with 404s

Covers: forms, posts, attributes, groups