s&box: Applying forces and impulses to Rigidbody — ApplyForce, ApplyImpulse, velocity

In s&box, applying forces, impulses, and reading velocity on physics objects requires the Rigidbody component API. Developers coming from Unity use AddForce/AddTorque but the s&box API uses ApplyForce/ApplyImpulse. Also, Rigidbody requires a collider on the same GameObject — without one, physics won't work.