R1:74cb7a8971a5

Add database configuration source to the source stack

Summary:
Read configuration from the new database source.

This adds an extra MySQL connect + query to every page. They're very cheap so I think we can suffer them for now, but I'd like to put cache in front of this at some point. The difficulties are:

- If we use APC, multi-frontend installs (Facebook) can't dirty it (major problem), and the CLI can't dirty it (fine for now, maybe a major problem later).
- If we use Memcache, we need to add…