Add sample or instructions for Google OAuth

[dalrympm]

I've extended the github example to include Google's OAuth2. I determined that by supplying the OAuth2RestTemplate to the UserInfoTokenServices I was able to get AuthenticationScheme.query used when retrieving the User Info. Applying the change to all ssoFilter() requests didn't seem to have any negative consequences but I could very well be missing something and would appreciate any feedback.

I've committed my own clientId and clientSecret that I've only used for this purpose, not sure what additional ramifications there may be for doing so.

Note that I did not make any changes to the TokenType (i.e. from Bearer to bearer) as mentioned elsewhere on the internets.

Fixes #5

[dsyer]

Google is a popular provider, so I'm sort of interested in this as at least a sidebar in the text (not sure if the code needs it, but it's pretty minimal., so maybe it's worth it). I'd be even more interested in a new sample app just for google that added some new features, like restricting authentication to a particular domain or something.