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)
Yep. I checked wherever these three were used together. 
Just to remind we need to go through all examples on confluence to make sure they are also compatible with the new naming convention!