R1:ba489f9d85f3

Add a local configuration source and a non-environmental ENV config source

Summary:
See discussion in T2221. Before we can move configuration to the database, we have a bootstrapping problem: we need database credentials to live //somewhere// if we can't guess them (and we can only really guess localhost / root / no password).

Some options for this are:

- Have them live in ENV variables.
- These are often somewhat unfamiliar to users.
- Scripts would become a huge pain -- you'd have to dump a…