First cut at recurring event exception API

This adds two calls to the calendar provider:

  insert(<baseURI>/exception/<original-event-id>)

This creates an exception to a recurring event.  Depending on the
values provided, this may alter all instances, all future instances,
or just a single instance of the event.

  delete(<baseURI>/exception/<original-event-id>/<exception-event-id>)

This deletes an exception to a recurring event.

Bug 4473786

Change-Id: I9bff5de24694dcd49d2036c6c99dd45b34b24c0f
4 files changed