R1:e2b6912b9dc7

Store "All Day" events in a way that is compatible with EditEngine

Summary:
Ref T11326. Normally, events occur at a specific epoch, independent of the viewer. For example, if we're having a meeting in 35 hours, every user who looks at the event will see that it starts 35 hours from now.

But when an event is "All Day", the start time and end time depend on the //viewer//. A day like "Christmas" does not start at the same time for everyone: it starts sooner if you're in a more-eastern timezone. Baiscally…