It should not be possible to drag a component from one preview into the other

Overview

If you click and drag a component in the Desktop preview iFrame and drop it in the Mobile preview iFrame it currently removes the component from Desktop and shows it where you dropped it in the Mobile view. This should not be possible.

Proposed resolution

When dragging starts in a iFrame, the other iFrame(s) should be greyed out so that the user cannot drop the component into them.

User interface changes