Media model api

Initial implementation and getting myself up to speed with the current code base. So far:
* Added `media` table with schema defined in the migration file [20131007103144.php](https://github.com/ushahidi/Lamu/blob/media-model-api/application/migrations/3-0/20131007103144.php)
* Added a `media` model. 
* Added media controller `application/classes/Controller/Api/Media.php` with some initial implementation for the various endpoints
* Added test for `media` model

**Next**
* Implement the actual file upload so it uploads the images to `application/media/uploads`
* Look into adding migration script for images.
* Write behat test to test the endpoints.
* Look into wiring the media endpoints when creating a post.
* Review feature