Cancel edit prior reparenting the applet

First go out of applet edit mode, get rid of the config overlay,
release mouse grabs in preparation of applet reparenting.

Depends from plasma/plasma-workspace!4053

deleting items that have the current mouse grab can cause weird
behaviors or crashes

CCBUG:482371
CCBUG:483287


(cherry picked from commit a4bf630e)

a4bf630e Cancel edit prior reparenting the applet