LOGIN-315 Add support for querying by endpoint location.

Provide /endpoints/<endpoint_url> endpoint for resolving an entity by an endpoint URL that matches a registered endpoint base URL. This facility is primarily intended for CAS protocol support. Entities are cached by the given CAS service URL, which is liable to cache the same entity under several different keys given the propensity for CAS service URLs to vary with ad hoc querystring parameters. A simple cache cleanup scheduled process has been developed to help mitigate cache entry growth caused by this facility.