Speed Packets Should Always Be Repeated

[KermMartian]

As discussed in KermMartian/CalcDCC#1, CmdrArduino should always repeat speed packets, but currently never repeats speed packets. The workaround for now is to simply just always post the latest speed, even if it hasn't changed, to the packet scheduler.

[johnnylingo]

I think it's easiest to take care of this in the front end for active locomotives, rather than the back end for all locos. I refresh speed packets for all active locos every 1/2 second.