Car class has the following functions:

-------waiting to be verified by Leyao Lee----------
    
    - start motor when motor signal on firebase is "on"
    - stop motor when motor signal on firebase is "off"
    - start alarm when alarm signal on firebase is "on"
    - stop alarm when alarm signal on firebase is "off"
    - start remote camera when camera signal on firebase is "on" and the power signal on firebase is "off"
    - stop remote camera when camera on firebase is "off" or the power signal on firebase is "on"
    - take a theif picture when item in front of the distance sensor for more than 5 seconds