R1:73991bb2621d

Added channel ID to events

Summary: Added a column channelID column to phabricator_chatlog.chatlog_event

Test Plan: Checked through mysql to see if table is updated

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D4956