Minor fixes and improvements

Drones now collect ore faster if there are asteroid fragments in the belt.
That means that you can get more or faster if you go and blow up some asteroids.

It's now also required to fight by your self in order to get the security level of the belt up. Drones won't go to unsafe belts.
I will later implement structures that you can place in belts, like gun towers, to make the belt safer.

Besides what I mentioned above, I fixed some bugs and started to implement some basic balancing.