RigidBodyPropellor.m

Adding RigidBodyPropellor.m. This adds both a thrust and a moment due to aerodynamic drag from a propellor spinning, allowing a quadrotor to directly control its yaw.
could really derive from SecondOrderSystem, and get a useful tools from that.
you'd have to change the dynamics method to qdd = sodynamics(t,q,qd,u)