Display current back EMF for tuning

[o_lampe]

Hi devs,
based on the "extrusion volume" thread, I also think a back EMF calculator as DWC plugin would be helpful for tuning.
The required parameters are almost completely known for the calculation. It only misses coil resistance and inductivity (AFAIK)

Since my Duet boards run on their own network, I don't have access to the EMF calculator at reprapfirmware.org

If we could integrate it as plugin and use 'live' values from the current object model/gcode file, we'd have a nice tuning tool