Scheduling: Multiple event scheduling nitpicks

[gregorydlogan]

Multiple minor issues:

• Multiple event scheduling allows scheduling events in the past. Single event scheduling (correctly) refuses to let me do this.
• Modal does not check if the date range, and day-of-the-week settings make sense.
  • I would expect settings like Monday and Tuesday, but restricting the date range to 25-01-16 -> 25-01-17 to throw an error in the UI rather than after the final submit to the backend
  • Assuming at least one day and date combination match things work as expected.
• Changing the hour (or duration) such that the end time is tomorrow does not display the date next to the end time the way that the single-event scheduling does. Obviously we can't put a date here, but something like + 1 day or something next to it would clarify.
  • Not supporting this at all would also be an option here. This functionality raises a bunch of fun edge cases.

Noticed in testing #1069