Event form fix 78188780

fixes the events new & edit forms so that they can manage the event's end date.
As part of this fix, also fixed some problems with the event model's end_time and schedule generation
I hope that the events model is solid now so that we can move forward more reliably.
https://www.pivotaltracker.com/s/projects/982890/stories/78188780
We don’t seem to have tests to cover the “attributes invalid” case here, let’s not forget that :wink:

On a different note… since this is very much an edge case… we shouldn’t have to worry about catching it. Ideally, this can be avoided by making `Event.transform_params(…)` stricter when it sanitizes the `params`. There is a huge improvement in readability when we can avoid errors rather than handle them.

I leave it up to you to decide which of these options you could choose. Once you have made those changes, it will be all good to merge. Ideally you could get this in before this time tomorrow, I am planning to push everything to Staging then.