R1:963485a3da25

Rescheduling events by dragging them in day view

Summary: Ref T8300, Rescheduling events by dragging them in day view

Test Plan: Open day view, drag events, observe them reschedule.

Reviewers: chad, epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin, epriestley

Maniphest Tasks: T8300

Differential Revision: https://secure.phabricator.com/D12988