Support ESP300 for non-ESP motors without encoders

[pkienzle]

We had an ESP-300 controller with one ESP-compatible motor and two non-ESP compatible motors.

The limit switches on our non-ESP stages were not connected. We used the ZH command to determine if the axes have active limit switches.

To get the number of axes we could not use the ZU command as given in the existing code. Instead we query each axis until we get an invalid axis error.

The scaling factor between movement distance and motor pulse did not work for non-ESP compatible motors without encoders. We added a condition for open loop with no encoder feedback to set the scale from full step resolution without a microstep correction.

Better error handling:

• Check for errors before retrieving position in set_status.
• Remove axis specification from TB and TE commands since there is a single error queue for all axes.