Update SchemaQuery and the web UI to accommodate multiple master databases

Summary:
Depends on D16115. Ref T11044. In the brave new world of multiple masters, we need to check the schemata on each master when looking for missing storage patches, keys, schema changes, etc.

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.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11044

Differential Revision: https://secure.phabricator.com/D16847