Server-side protocol support needs simplification

[awkay]

We should be able to make the server-side bits easier. The basic idea would be to make it possible to write the test as:

(helper/with-db-fixture user-db
     (let [server (server/make-untangled-test-server
                    :parser demo/server-parser
                    :parser-injections #{:user-database}
                    :components {:user-database user-db})]
       (specification "Server tx executes properly"
         (behavior "Adds user to database"
           (ps/check-response-to-client server add-user-protocol))))
     :migrations "app.sample-migrations"
     :seed-fn user-seed)

where tempid remapping (seed results) could be found by scanning the parser injections for databases (and use (:seed-result (get-info DatabaseComponent))).

There are two major changes that need to be made for this to work right:

• Make it so that start on a DatabaseComponent is idempotent (so we don't try to restart it)
• Collect ID remaps from all of the databases injected into the parser so that ID support works properly.

I'd suggest we make a new method and deprecate the old, since there are existing users of the old support.

[awkay]

Oh wait: one more unsolved problem. The seed function in this case does not have proper integration with the protocol data. So, at attempt to access a pre-existing thing on the server is kind of tough. Perhaps this isn't easy to simplify further.