Cannot drop someday event on all-day row

[tyler-dane]

Where did this happen?

Self-hosted (yourdomain.com), Hosted (compasscalendar.com)

Expected Behavior

Able to drop a someday event to the allday row after dragging and hovering over all-day row

Current Behavior

Problem 1: Cannot place event over allday row when dragging

Problem 2: When release event from someday event drag, the event is "dropped" onto the timed grid (instead of returning to its place in the sidebar)

allday-drop-bug.mov

Steps to Reproduce

1. Create someday event on week view
2. Try dragging it over to the all-day row
3. Notice: the all-day event placeholder doesn't show up like it should 👎
4. Move the mouse over the heading
5. Drop
6. Notice: a long timed event is created 👎

Possible Solution

Restrict mouse movements to valid dropzones, similar to the expected behavior from #1786

Context

This is bad UX that'll cause users to drop