R1:973079a7da3d

Modularize application configuration panels

Summary:
Ref T7149. This is a few steps away, but:

- Generally, I'd like to reduce the amount of "Config" configuration we have.
- One good way to do this is to move it into UIs in Application configuration. We did this with email recently.
- I think this was a great change and I'd like to keep moving in this direction.
- T7149 touches configuration related to file storage engines. Although I'm not planning to fully move configuration into applications…