Rename "Force" to "Actuation".

(to make naming more consistent and descriptive; including functions such as getForce, setForce,
computeOverrideForce, overrideForce, isForceOverriden, setOverrideForce, getOverrideForce)
`get/setActuation` should not be virtual. You are implementing the caching here, so it is unnecessary for other scalar actuators to override. Same is also true for speed. Compute actuation should `setSpeed`. It doesn't make sense for a caller to set the speed of the actuator. This was all inherited from code where the difference between a public interface and the extensibility (developer) interface were completely blurred. This is would be a good first step at correcting.