Properly import all-day events in Calendar

Summary: Ref T10747. The transaction version of this copies the "all day" flag over properly, but this non-transaction version needs to copy it explicitly.

Test Plan: Imported an all-day event, saw it come in as all-day.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10747

Differential Revision: https://secure.phabricator.com/D16770