Merge branch 'states' into sz/maintenancestate
Merge branch 'master' into sz/maintenancestate
First GUI implementet. Working. New methodes in controller for accesing the gui display.
Merge branch 'master' into sz/maintenancestate

Conflicts:
	src/main/java/ch/zhaw/id5848/parkingmeter/core/ParkingMeterController.java
	src/main/java/ch/zhaw/id5848/parkingmeter/core/states/ReadyState.java
	src/main/java/ch/zhaw/id5848/parkingmeter/core/states/State.java
make tests pass