Calendar tooltips should always show start and end time of events.

Summary: Closes T8191, Calendar tooltips should always show start and end time of events.

Test Plan: Open month view, hover over, All day events, multi-day all day events, multi-day non-all-day events, and regular events. Tooltips should be "All day", "All day, <start> - <end>", "<start>-<end>", and "<start>-<end>", respectively.

Reviewers: epriestley, #blessed_reviewers, chad

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin, epriestley

Maniphest Tasks: T8191

Differential Revision: https://secure.phabricator.com/D12846