Management of RFC6749 errors

This pull request includes some fixes about management of rfc6749 errors:

- First, check duplicate parameters
- Missing parameter is invalid_request error according to rfc6749
- mismatching_redirect_uri, missing_redirect_uri,invalid_redirect_uri are not defined in rfc6749 or OAuth Extensions Error Registry
- Check if response_type is present with a valid value according to rfc6749, then check if client is authorized
There is not an invalid_client_id either :) All fatal ones I made up as none should be returned to the client and served only as pseudo descriptors.