Update SchemaQuery and the web UI to accommodate multiple master databases
This realigns all the "check out what's up with that schema" calls to work for multiple hosts, and updates the web UI to include a "Server" column and allow you to browse per-server.
This doesn't update bin/storage, so it breaks things on its own (and unit tests probably won't pass). I'll update that in the next change.
Test Plan: Configured local environment in cluster mode with multiple masters, saw both hosts' status reported in web UI.
Reviewed By: chad
Maniphest Tasks: T11044
Differential Revision: https://secure.phabricator.com/D16847