P0-B2: Part 1085: Improvements, Debugging

Ringworlds are now basically done, at least for the moment.

I fixed an issue with object placement, which was actually a pre-existing issue that was causing less obvious issues with planetary object placement too, so I fixed two issues at once.

I have also added the ability to control whether or not cities and outposts spawn on a particular planet or ringworld.

There are some minor issues still with the ringworlds, but I can fix these later.