Fix issue with number scrubber/color picker becoming unresponsive

The problem was that we were appending them to the elements and then when we
deleted the elements, we lost the events on them. Appending them back to the body
when hiding fixes the issue.

Test Plan:
- Drag a rect over, change the numbers, delete the rect while the number picker is open,
drag in a new rect, change the numbers

Auditors: john