Give "Config" a full-width, hierarchical layout
Subsections are now in a landing page console and groupings have been removed. We "only" have 75 values you can edit from the web UI nowadays, which is still a lot, but less overwhelming than it was in the past. And the trend is generally downward, as config is removed/simplified or moved into application settings.
This also gets rid of the "gigantic blobs of JSON in the UI".
Test Plan: Browsed all Config sections.
Maniphest Tasks: T13362
Differential Revision: https://secure.phabricator.com/D20934