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

src/docs/technical/ircbot.diviner

@@ -50,6 +50,8 @@ the IRC bot. These are the default handlers available:
   - @{class:PhabricatorIRCDifferentialNotificationHandler} This handler posts
     notifications about changes to revisions to IRC to the channels listed in
     ##notification.channels##.
+  - @{class:PhabricatorIRCLogHandler} This handler records chatlogs which can
+    be browsed in the Phabricator web interface.
 
 You can also write your own handlers, by extending
 @{class:PhabricatorIRCHandler}.