add stepper rotation commands

[aksell]

The claw_stepper only has directional control at the moment. It could be useful to give a command to perform a given amount of rotations/steps for spinning valves and such. It could be especially useful when attempting to level the OBS when we know how many rotations are needed to level the platform.

[sindrehan]

This is a good idea. Will be practical to be able to ask for x number of degrees (or radians, if you're a nerd).