Load Provider Settings from Datastore

[kylefinley]

Proposed here by Nick R

Developers should be able to store providers settings in the datastore.

Possible implementation details

1. A request is made to a service i.e. example.com/auth/provider
2. A check is made to the appengine_config.py.
3. If no settings are found. A check is made to a NDB provider model.
4. If no model is found. A new NDB provider model is saved to the datastore with empty settings. This will make it easier for a developer to add settings.

Efficiency

Using NDB models will make the retrieval very efficient. Request will follow this pattern instance => memcache => datastore

Multiple Hosts

To allow for multiple hosts the key for the Providers should use this form domain:provider E.g. example.com:google or example.com.br:google.