Add ACL and login

Adds a basic access control and authentication layer.

What this does
* [x] Replaces core auth module with A1 and updates that to use a better bcrypt library
* [x] Add login/registration controller and check for logged in user in /oauth/authorize
* [x] Add A2 and ACL modules
  * [x] Use a2 config to set default application permissions for each resource
* [x] Add generic access checks to Ushahidi_Api Controller
* [x] Abstract resource loading in each api controller so we can get the resource (post/form/user/tag/etc object) and use this is the access checks
* [x] Demonstrates complex access checks for posts (based on parent access, and published status)
* [x] Basic access checks for other models: tags, forms, attributes, users, sets
* [x] Add access tests for posts
* [ ] Add basic tests for access to other API calls

Not implemented / Postponed:
* Complex form, form group, form attribute permissions #32 
* Complex user permissions #64 
* Tag permissions #56 
* Doesn't anyway to dynamically set permissions through the DB. #65 This should be post MVP along with #18