Respect 12 hour vs 24 hour time formats in Calendar day views
Summary: Fixes T9202.
Test Plan:
- Viewed day in 12-hour, saw "8:00 PM".
- Viewed day in 24-hour, saw "16:00".
Reviewers: chad
Reviewed By: chad
Maniphest Tasks: T9202, T10932
Differential Revision: https://secure.phabricator.com/D16290