Improve spaceship movements

[aromanro]

Currently following a movement command, the spaceship rotation accelerates up to a certain angular velocity then it rotates with a constant angular velocity (if the angle is large enough, otherwise this constant velocity won't be reached), then it decelerates up to the target angle, it rests there for a little while then it turns back orienting itself in the direction of the camera.

The problem is that a new command during this time will interfere with the movement, because the code takes into account only the spaceship orientation, but not the angular velocity when a new orientation is required.

This obviously can be improved.
It's quite boring stuff so I probably won't change it for a while.