Summary:
countdown_timer table named to countdown.
datepoint and related stuff renamed to epoch.
Countdowns now have phids.
Various UI items changed from timer to countdown.
Test Plan: Did run storage upgrade and added some countdowns.
Reviewers: epriestley
Reviewed By: epriestley
CC: aran, Korvin, AnhNhan
Maniphest Tasks: T2624
Differential Revision: https://secure.phabricator.com/D5812
