Reworked gravity anchor

When gravity anchor is on, the ship moves very slowly but is much more stable. When it's off, the ship can move as quick as it wants but the controls are extremely hard to use, although it's more realistic. I'm suggesting a complete rework of how the gravity anchor works, so more people would want to use it.

This would introduce one new module, called thrusters, that would improve the speed at which you accelerate, and improve improve your max speed when GA is on. Boosters would increase your ship's max speed by 100 m/s per level.

In addition, the turning speed of ships would increase drastically. The goal of this is to make the ship move like in other Sci-Fi games such as Galaxy on Fire 2, where you don't have to watch your ship drift off into the distance or spin endlessly if you don't stop it manually.