R1:f24318f3086a

Make "profile menu" configuration mostly work

Summary:
Ref T10054. This does a big chunk of the legwork to let users reconfigure profile menus (currently, just project menus).

This includes:

- Editing builtin items (e.g., you can rename the default items).
- Creating new items (for now, only links are available).

This does not yet include:

- Hiding items.
- Reordering items.
- Lots of fancy types of items (dashboards, etc).
- Any UI changes.
- Documentation (does feature: TODO link for…