Simplify Config loading

[bfops]

Config loading right now is error-prone and finicky. Changing parts requires changes in multiple locations. Fix

[bfops]

Config broken into separate pieces in 01e32bb (merged in 711711f)

[bfops]

Merging Config and ConfigLoader would be the next step, and avoid prefetching all the values. But then we would want to cache any already-fetched values, and we would end up with this setup again