Motor constants setter only called when full motor constants object is supplied instead of at attribute change

[tkevinbest]

@senthurayyappan I found an issue with how I did this. The setter method is only called when assigning entirely new motor_constants objects. If you try to just write to one of them like osl.ankle.MOTOR_CONSTANTS.NM_PER_AMP = .1, the setter logic doesn't get called. I think we can fix this with __setattr__ overloads or something like that...

Originally posted by @tkevinbest in #489 (comment)

[tkevinbest]

@rgpieper want to try to fix this? We somehow need to trigger a recalculation of all derived motor params when any of the properties in MOTOR_CONSTANTS is written to. Hopefully there's a clean and elegant way to do that.

Once it is fixed, we can add a unit test. The resolved issue should pass something like:

pre = osl.ankle..MOTOR_CONSTANTS.NM_S_PER_RAD_TO_MOTOR_UNITS
osl.ankle.MOTOR_CONSTANTS.NM_PER_AMP = .1
assert (osl.ankle..MOTOR_CONSTANTS.NM_S_PER_RAD_TO_MOTOR_UNITS is not pre)