Allow for user to provide redirectURI for OAuthClient

[kayvank]

Allow for user to provide a callback url as outlined in google oauth dos:
Currently the redirectURI, callback, is a hard-coded value of: callback, redirectURI

Allow the user to provide their own callback. This will allow the users to avoid the manual cut/paste of the oAuth code and provide a smoother user interface.
If accepted, I'll be happy to work on this task