Don't try to move when there's no speed
Add and use an MWWorld::isFlying method
Don't try to step if not on the ground
Handle levitate and swift swim effects
Allow stepping when not being affected by gravity
Update animation looping when setting the same state
Update the PhysicActor's RigidBody when moving

This works, but is less than ideal. As it is now, the rigid body gets updated
twice as the position and rotation are set separately. They should instead be
updated together.