Calendar events should now have a 'Name' field.

Summary: Closes T7953, Calendar events should now have a 'Name' field.

Test Plan: Create or edit event with no title, save event, should get error requiring name, event detail view timeline should reflect name changes.

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: Korvin, epriestley

Maniphest Tasks: T7953

Differential Revision: https://secure.phabricator.com/D12591