Expose ship class base stats

[twof]

Useful for various physics calculations

Accessible in game via

class().default_stats()

[twof]

@rlane Alright I think we're good to go. Not sure if it's exactly what you meant, but I implemented From<ClassStats> on ShipData. I'm still pretty new to Rust, but that felt like it was a good way to do it. Let me know if you want any other changes!

[rlane]

Thanks!