Re-do causes crud.

Cause CRUD is now /api/cause_type instead of /api/cause. 
Each cause type also now has an image URL and an image provider.

**GET /api/cause_type** 
  * gets all causes

**GET /api/cause_type/&lt;key&gt;**
  * gets a specific cause

**POST /api/cause_type**
  * creates a new cause / updates an existing one

{"name":"homeless", "image":{"url":"https://graph.facebook.com/100006074376957/picture","urlProvider":"FACEBOOK"}}

**DELETE /api/cause_type/&lt;key&gt;**
  * deletes a specific cause type