public.json: Add 'route' query parameter to 'GET /drops'

So you can figure out which drops belong to a route.

Internally, we have additional metadata for each association
(e.g. sequence numbers to order drops along each route), but I don't
think folks using the public API will care about that on a per-route
level.  We probably do want sequence, delivery-offset information,
etc. for route-trip <-> drop associations, but we'll get to that
later.
public.json: Add 'drop' query parameter to 'GET /routes'

So you can figure out which routes service a drop.  The mirror of
313a1ccb (public.json: Add 'route' query parameter to 'GET /drops',
2014-11-14).