server_actor.rs had grown past twelve hundred lines, a fifth of them
tests and a hundred the value types it hands out. The types now live in
server_actor/types.rs and the tests in server_actor/tests.rs, as the
client's already do, and the room and user traffic in handle_message
moves to its own dispatch step beside the wishlist one. No behaviour
changes; the public paths are re-exported as before.
