Collision physics

[Norgg]

Have collisions rebound objects, allow the ship to survive very slow collisions.

Some work has been done on this in the debris-angular-collisions branch but it needs re-thought and gone over.

[Riot]

We have forces and non-destructive collisions. Do we still want to implement low-speed collision survival for the player ship?

[Norgg]

Would be nice to have angular momentum from collisions working, but seems unlikely that'll make it in.

I'll open a new issue for low-speed collision survival.