R1:64d6593e9cba

Modernize pinned homepage applications settings

Summary:
Ref T4103. A few bits here:

- We have an ancient "tiles" preference which was just a fallback from 2-3 years ago. Throw that away.
- Modenize the other pinned stuff. We should likely revisit this after the next homepage update but I just left the actual defaults alone for now.
- Lightly prepare for global default editing.
- Add a "reset to defaults" option.

Test Plan:
- Pinned, unpinned, reordered and reset application homepage order.