Add hover outline for selectable annotation objects

There is now a text color/background color dashed outline around the visualGeometry of hovered visible EditActions. I implemented it using a QML item instead of in the paint event because it repaints faster at high zoom levels that way. It might be a bit troublesome to change if we ever want to switch to more tightly fitting outlines instead of simple rectangle outlines.

Still visible at different zoom level and on different backgrounds: