Summary:
Ref T1163. Ref T2625. This could probably use some tweaks, but I kept things mostly-generic.
I added a new control for freeform dates so we can have it render help or whatever later on.
Test Plan: See screenshots.
Reviewers: chad, btrahan
Reviewed By: btrahan
CC: aran
Maniphest Tasks: T2625, T1163
Differential Revision: https://secure.phabricator.com/D6084
