Calendar events should be supported in global search

Summary: Closes T7937, Calendar events should be supported in global search.

Test Plan: Search for part of calendar event title in global search, event should be in search results.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T7937

Differential Revision: https://secure.phabricator.com/D12636