endpoint for aggregate status list as from the spec #96
Description
Implement the endpoint and update readme as from this section in the spec https://www.ietf.org/archive/id/draft-ietf-oauth-status-list-10.html#name-status-list-aggregation.
Also, it looks like support for the optional aggregation_uri field in the StatusList model is missing as defined in Section 9.2 of the spec.