Unless the mouse pointer is not next to an electric border kwin calls
Outline::hide() on every move/resize event. To avoid unnecessary
repaints we now check whether the outline has been visible or not.
This change unduplicates some code and merges it into one class
allowing us to use an replacement effect for the outline in
future.
CCMAIL: a.arlt@stud.uni-heidelberg.de
REVIEW: 100848