tilt the position of the actuators.

[syhaffert]

This is an extremely minor bug fix for tilted DMs. In the original implementation the pokes themselves were tilted by stretching or compressing the pokes. However, the actuator positions also have to be modified. I added the x, y and z parameters to the actuator position function.

[ehpor]

@syhaffert Tests are failing on the actuator positions.