Add a basic chatlog

Summary:
This is pretty simple and unpolished, but it's getting pretty big and it seems
like a reasonable starting point.

• Log chat in various "channels".
• Conduit record and query methods.
• IRCBot integration for IRC logging

Major TODO:

• Web UI is really unpolished and has no search, paging, anchor-linking, etc.

Basically all presentation stuff, though.

• I think the bot should have a map of channels to log with channel aliases?
• The "channels" should probably be in a separate table.
• The "authors" should probably be correlated to Phabricator accounts somehow,

where possible.

Test Plan: Used phabotlocal to log #phabricator.

Reviewers: kdeggelman, btrahan, Koolvin

Reviewed By: btrahan

CC: aran, epriestley

Maniphest Tasks: T837

Differential Revision: https://secure.phabricator.com/D1625