Make settings panels more modular and modern
Summary:
Currently, we have a hard-coded list of settings panels. Make them a bit more modular.
- Allow new settings panels to be defined by third-party code (see {D2340}, for example -- @ptarjan).
- This makes the OAuth stuff more flexible for {T887} / {T1536}.
- Reduce the number of hard-coded URIs in various places.
Test Plan: Viewed / edited every option in every panel. Grepped for all references to these URIs.
Reviewers: btrahan, vrana, ptarjan
Reviewed By: btrahan
CC: aran
Differential Revision: https://secure.phabricator.com/D3257