Summary: We will need it for two purposes: - Status tool. - Nagging tool - @aran suggested using "3 business days" and I don't want it to fall on New Year's Eve or such. I don't plan working on any interface for editing this as this kind of data should be always imported. Test Plan: `bin/storage upgrade` `scripts/calendar/import_us_holidays.php` /calendar/ Reviewers: epriestley Reviewed By: epriestley CC: aran, Koolvin Differential Revision: https://secure.phabricator.com/D2375