R1:c7f2e4a9246e

Document calendar summary icons

Summary:
Fixes T11809. Ref

- Explicitly document the summary icon hints -- I don't think these are too hard to figure out (and maybe this stuff should just go in the tooltips) but we can start here.
- Use color + shape to distinguish between "cancelled" and "declined", not just color (for users with vision accessibility issues).
- Translate a "minute(s)" string into sensible English.
- Use RSVP status on the month view green circle thing.

Test Plan:
- Read docs.