testing out speed calc from position for api use

this may work for api calls like, rotateTo() or rtz()
add live speed slider adjustment feature for motor

This (in a little smoother form) could also replace the current speed
slider action, but it was intended so that the slider can adjust the
speed smoothly while a motor is running (so you can gradually
accelerate), rather than incrementally (i.e., speed only adjusts when
you release the slider bar)
main.js gang live speed adjust

added live speed adjustment with the slider bar for while a gang's
motors are in motion
Merge branch 'John'