Add ScnObservable class with setChangedAndNotify() function
The ScnObservable extends the normal Observable with the combined setChangedAndNotify() function
Refactored RadioMediumObservable and added new Observable
Refactored RadioMediumObservable to RadioTransmissionObservable because of its function
Added correct RadioMediumObservable and updating in AbstractRadioMedium, DirectedGraphMedium and MRM
Added some documentation
settingsObservable superseded by radioMediumObserver
Wasn't used anyway