Make URMP force/torque values optional

If 0, they won't override the part.cfg's values.
Update example cowling

Remove the dynamic breaking force/torque values, since they don't really
apply for a surface-attached interstage.
Add support for duplicate mesh names

Allows MovingSegment to control specific meshes when they're duplicated.
Add example interstage with duplicate part names
Fix off-by-one error in parsing
Add a URMP Upper example part
Correct sample part name