Make chatlog a bit less awful
Summary:
- Default to showing the newest page of chat.
- Reformat for greater readability.
- Add permalinks to specific lines.
- Enable jump-to-date.
Test Plan: {F12200}
Reviewers: Koolvin, vrana, btrahan
Reviewed By: btrahan
CC: kdeggelman, aran
Maniphest Tasks: T837, T1065
Differential Revision: https://secure.phabricator.com/D2641