[WIP] Limit ship's jerk by 1g/s

[Mc-Pain]

This will affect:

• Autopilot
• Manual ship control
• Missiles
• NPC ships (?)

This will disallow accelerating instantly from standing still to full thrust.
Instead, full thrust will be applied after several seconds, increasing or decreasing linearly.

• Autopilot is broken: ship will never reach its destination, orbiting this point instead.
• Suggestion from IRC: load jerk limit from ships JSON instead of fixed constant of 9.8 m/s^3