A simple gateway to store incoming email messages, and notify the intended recipient via GCM.
The GCM notification includes a url from which the rest of the message can be downloaded.

The intent is to use this gateway to deliver mail messages to Klaxon (http://code.google.com/p/klaxon).

GCM docs: http://developer.android.com/google/gcm/index.html

Useful URLS:
- /register - used by devices to register with the service.
  - Args: 
    - token - GCM registration id.
    - sender - email address that is authorized to send GCM messages.
- /test - debugging. sends a push message to the current user, assuming they are already registered.
- /admin - a simple interface to allow the inputting of credentials for the sender of GCM messages.
  - You should use the api_key method for use with GCM.
  - The username and password fields are vestigial, from c2dm.


The Anatomy of a C2dm Message:
- registration_id
- collapse_key
- data.from
- data.subject
- data.body
- data.url