This PR changes "Force" to "Actuation" for all relevant Actuator's member functions.

(to make naming more consistent and descriptive; including functions such as getForce, setForce,
computeOverrideForce, overrideForce, isForceOverriden, setOverrideForce, getOverrideForce)
So, the way an Actautor works is that you override computeForce and you call setActuation to set that force/torque? I think this is fine for this PR, but this way of writing Actuators seems somewhat confusing.