OAuth 2.0 App Engine Authentication

[jcricket]

Create Mechanisms for accessing secured GWT RPC methods using OAuth 2.0 credentialing services. For Android, using GoogleAuthUtil is the expectation. Will need to create a way for RemoteServiceServlets to utilize this data since GAE only supports OAuth 1.0 UserService, which is itself only in beta.

[jcricket]

branch gae_auth has manually tested, functional code for utilizing OAuth 2.0 credentials from Android against GWT RPC.