R1:61f82bb97b8a

Introduce "Curtain" views, panels, and extensions

Summary:
This opens up the new action column to have specialized rendering and behavior. Briefly:

- Converted applications (right now, only Paste) render a `CurtainView` to build the column content.
- This view uses new extensions to build panels (projects, subscribers, tokens).
- The panel extension code and rendering can be changed without breaking old stuff.

Minor changes:

- Token awards now load their tokens, for consistency/simplicity.