Bit of progress here !

- I separated concerns of model and controller
- tried that hovering/leveling again from scratch and it seems it's a better route -> leveling is coherent and it is now unaffected by a tunnel whereas previously it was going crazy (@tigrou seems like I'll need your air tip at some point !)
- also hitting walls is coherent as well though it will certainly need a different physic material to behave like the original game
- edit : I do constrain rotations now

The simplest approach works the best !! The feeling is definitely Wipeout-like when the ship raises/lowers its nose, will need a few magic values later.

For BallisticNG code however, I've abandoned for now as it's too early, I'll certainly take higher-level hints from it but at this point I was not feeling that simply fixing the errors will do the job, plus many constants were missing as well.

So a little victory but definitely more positive than the stalling of last days