Add a 200ms delay when dragging a meta box on mobile devices, to prevent...

Add a 200ms delay when dragging a meta box on mobile devices, to prevent inadvertently dragging meta boxes around on a touch screen.

props helenyhou, georgestephanis. fixes #20557.



git-svn-id: https://core.svn.wordpress.org/trunk@20614 1a063a9b-81f0-0310-95a4-ce76da25c4cd