Summary: you can now add, edit, and delete status events. also added a "description" to status events and surface it in the big calendar view on mouse hover. some refactoring changes as well to make validation logic centralized within the storage class.
Test Plan: added, edited, deleted. yay.
Reviewers: epriestley, vrana
Reviewed By: epriestley
CC: aran, Korvin
Maniphest Tasks: T407
Differential Revision: https://secure.phabricator.com/D3810
