Show user status on calendar

Summary:
This is a rough cut, but gets some of the basics at least. Here's what it looks like:

{F11690}

Some things that would be nice for future diffs:

• Different colors for different event types (tasks? MEETINGS?!)
• When events span across multiple days, keep them in the same row.
• Switch which month you're looking at.
• Show specific users instead of all.
• etc etc etc

Test Plan: See screenshot.

Reviewers: btrahan, vrana

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D2514