Change the way how screen edges interact with Effects/Scripts

The main difference is that the activation of an edge is no longer
broadcasted to all effects and scripts, but instead a passed in slot of
the Effect/Script is invoked.

For this the EffectsHandler API is changed to take the Effect as an
argument to (un)reserveElectricBorder. As callback slot the existing
borderActivated is used.

In addition the ScreenEdge monitors the object for beeing destroyed and
unregisters the the edge automatically. This removes the need from the
Effect to call unregister in the dtor.

BUG: 309695
FIXED-IN: 4.11