[Implemented] Canceling SOS call

[◄Chuck►]

Just imagine that "helping civilian" had a tow tag. What difference would it make to you? You still drove across the track just to notice there is no work left for you.
However, a "cancel" buttons seems useful anyway.
One last word: You don't need to feel obliged to drive across the entire track when its clear that other cars are way closer to the caller. That's what I think is "professional", to pick-up that word again.