Calendar event edit view should validate that start time preceeds end time

Summary: Closes T8023, Calendar event edit view should validate that start time preceeds end time .

Test Plan: Create Calendar event, add details, make end time be earlier than start time, try to save, get error, make sure all previously entered details are populated correctly.

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: Korvin, epriestley

Maniphest Tasks: T8023

Differential Revision: https://secure.phabricator.com/D12656