Fix exception handling in SearchServiceImpl.tryAsExactStop().
Use a multimap for short name-to-id and long name-to-id for multi-agency cases where multiple distinct routes have the same short name.

This still needs UI implementation so that the frontend works properly when a short name query matches multiple routes.  Perhaps we should send the agency-and-id? (But then how do we distinguish a stop agency-and-id from a route agency-and-id?)