Throttles: Make emergency stop default when no heartbeat comes in even if it has not been requested by the throttle

[habazut]

Investigate how heartbeat is implemented and do stop any active loco unless the throttle does say it does NOT want that.

Heatbeat incoming               Active Loco(s)             Emergency stop requested by throttle             What we do
yes                                                                                                                                                    all fine
no                                         no                                 unknown or yes or no                                     does not matter
no                                         yes                                do stop                                                           stop all
no                                         yes                                no stop                                                           no stop
no                                         yes                                unknown                                                        stop all

Think this trough for Withrottle and DCCEX protocols.

[Asbelos]

Beware complex scenarios with locos handed off, or being run by other throttles when throttle is closed.