Replaced method swizzling with IDEBuildOperationDidStopNotification observer

I am in the process of adapting Warning Lights to use a different light and have done some optimisation.

The `IDEBuildOperationDidStopNotification` works in the testing I have done and is a lot less intrusive than the existing method swizzling.

I don't have a Phillips Hue so I haven't been able to check that this actually works with the lights but I haven't changed anything to do with the lights so I don't see why there would be a problem.