rework brew() and backflush()

clean up and less states for brew() and backflush()
removed brewOn and used bool brew()
removed manualFlushOn and used bool manualFlush()
move all backflush related stuff into brewHandler
fix includes for brewHandler.h
backflush() is now only called if mashineState is kBackflush
if mashine is in kBackflush brewswitch controls backflush and it is not possible to start a brew
removed boolean, use bool

moved PID and Heater disable into mashine state kBachflush