GET for contacts

URL for a single resource: /api/2/contacts/<contact_id>
URL for a collection: /api/2/contacts

Permissions Required for the API Key: 
* Overall Admin Level = Admin
* Manage Organizations and Contacts = Read (or Read/Write)

Filter Options for a collection (query string vars):
* 'catid' (integer, a category id. Limit results to contacts assigned to the indicated category)


