Minisystems, thrust, and friendlypopulate()

This update doubles the strength of the continous thruster.  It should be 1 to 1 with the pulse thruster mode in terms of oomph per thruster energy used.

I also added a new function ( generateminisystem() ) to the system class that generates a small system with a few inner planets only.  In the process of doing that, I squashed a bug in friendlypopulate() that would hang the game on startup if a system had too few planets to give new friendly NPCs a patrol route.  Rather than restrict systems or NPCs to compliant numbers of planets or patrol routes, friendlypopulate() will now just skip adding a group of traders or mercenaries if there isn't enough planets to make the patrol route.  This might ultimately result in the generateasteroidsystem() function becoming more of a general purpose system generation tool, as I previously struggled with the same problem when setting some parameters to 0 (such as number of asteroids, number of inner planets, and number of outer planets).

I also added some disorder to the system locations in the overworld.  So it's not obviously a grid anymore, but if you're looking for it you can easily tell that it's just a grid with a bit of randomness.   I hope to have a better method for placing systems in the future, but this is less cringe than it was before.