Add internal motor step counter to DUT_MotionStage

[wnwright]

Would be useful to have a way to track the motor steps according to TwinCAT. For example, this is useful information when determining an encoder scaling factor. As it currently stands, in order to track this, the engineer has to open the CoE parameters:

This only refreshes when the engineer scrolls. It would be nice to easily add this information to the ADS Symbol Watch

[ZLLentz]

Implementation-wise, we can either add an integer input to DUT_MotionStage and expect PLC projects to link to one of the standard PDO points explicitly, or we can try to read from the CoE cyclically.