Work-in-progress schema for Facts app

Summary: See discussion in D3078 for why I've separated this. Pretty sure it's not quite ready yet -- I want to build a couple of things on it so we have a better idea of what we need (autoincrement ID? <factType, objectA, epoch> primary key? objectB column? valueZ?) and don't need to do a ton of schema patches.

Test Plan: Applied patches, ran D3078.

Reviewers: vrana, btrahan, majak

Reviewed By: vrana

CC: aran

Maniphest Tasks: T1581, T1562

Differential Revision: https://secure.phabricator.com/D3088