add motor types

[laurb9]

See if it makes sense to combine stepper characteristics into a Motor class to be used by the driver.
Inductance, current, voltage, steps from the spec sheet give max rpm, for example: http://www.daycounter.com/Calculators/Stepper-Motor-Calculator.phtml

Or maybe having all that stuff in a class makes it more obvious which device the numbers refer to. We can replace the STEPS parameter with a Motor object.