Change es.GetEvents to use ES rather than query db. Strip down the private EventsQuery method - now only used to get instances. Can probably be stripped even further.

Add a couple of static RecurringRetrievalMode objects. Avoid object creation when we can use an immutable object.

Add RecurringRetrievalMode to indexer search - indicate if we want expanded events as we do mostly for the public calendars, or master + overrides.