R1:6eaa9faec77b

Provide default view and edit policies in Calendar, plus "Event Host" and "Event Invitees"

Summary:
Fixes T9224. This adds:

- A "Default Edit Policy" and "Default View Policy" to Calendar, similar to other applications.
- "Event Host" and "Event Invitees" objects policies.

These policies often end up being redundant (the host can always view/edit, the invitees can always view), but they can be more clear than setting "No One", and "Editable By: Event Invitees" is a legitimately useful policy.

Test…