R1:e4c6ae534518

Smooth out various transaction/editing behaviors for Calendar

Summary:
Ref T11809.

- Allow users to remove the "Until" date from recurring events.
- When removing "Until", show a sensible string ("...set this event to repeat forever.")
- When users go through the "Make Recurring" workflow, don't require them to explicitly select "Recurring: Recurring" from the dropdown. This intent is clear from clicking "Make Recurring".
- When editing "All Future Events", don't literally apply date changes to…