Summary:
Gets rid of `Config.get` in favor of three methods with names that express intend. The logic for applying defaults was used from one callsite only, and was moved there.
This is the starting point to make the config loading system a better place, including a strong return type and defaults always applied.
Reviewed By: martinbigio
Differential Revision: D4985774
fbshipit-source-id: 98300547c3eafd5948814d57ce93e71d43572eb8