Fixed an error calculating a distance, switched - to +.
GA now takes pylons into account, and only places buildings in legal positions.
Added support for fixed (unmoveable) buildings in GA. Config doesn't support it, so for now we just a hardcoded nexus.
Fixed 2 problems with repairing genomes: 1) The spiral search for legal building positions could overflow, now we only search on a small radius, 2) when repairing, pylons don't check if the other buildings are powered, we rather let the other buildings move toward the pylons instead of the other way around.