Incorrect redirect_uri in getAccessFromToken causes failure

Fixed case where the redirect_uri for getAccessFromToken is incorrect, causing OAuth to complain about an invalid redirect uri, and fail whatever action.

This mainly caused problems behind load-balancer where URI that was detected was incorrect (ex: would point to a local hostname). There was no interface to change this.

What I did:

* Added new parameter to constructor for redirect_uri, to set it instance-wide. 
* Refer to $this->redirect_uri, unless it's overriden (backwards-compat)
* Fixed the call to getAccessFromToken where it was passing '' and the strict === null would fail, but looks at $this->redirect_uri

As an aside, this also fixed my error with "CSRF state token does not match one provided.". I'm still not 100% clear as to why, but that might have just been an additional symptom.