DRAFT: refactoring for different reasons...

[mschmiedel]

• have everything related to the SAIC API in one class
• have the mqtt stuff a bit more readable
• make VehicleHandler and VehicleState much smaller (SRP).
• IMPORTANT: be able to bring all the MQTT command handling together and be able to do stuff like "if remoteTemperature is set and remote AC is currently on, then resend AC command with new temperature to car"... -> Closes Add HVAC / Rear Window Heat temperature controls #50

@tisoft, I separated this from the rest as it is a "bigger" restructuring, however I think it is a good idea to get the different functionalities better isolated and thus callable from different places without issues.