Improved CommandPruneDimensions. Cleaned up the code and improved
performance by using a HashSet instead of an ArrayList to list dimension
reachability. Added an optional argument that sets whether we should
delete the folders of pruned dimensions.
Made progress on overhauling and prettifying our commands. There are
still more changes to be done for this to be functional. I need to do an
intermediate commit because I want to merge in recent changes by Steven.