Store more datetime information on Calendar transactions and improve rendering behaviors

Summary:
Fixes T11805. Depends on D16785. This generally tries to smooth out transactions:

• All-day stuff now says "Nov 3" instead of "Nov 3 12:00:00 AM".
• Fewer weird bugs / extra transactions.
• No more silly extra "yeah, you definitely set that event time" transaction on create.

Test Plan: Edited events; changed from all-day to not-all-day and back again, viewed transaction log.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11805

Differential Revision: https://secure.phabricator.com/D16786