Improve UX for creating new levels

The most common question, and actually virtually the only thing that doesn't make sense instantaneously, is the "<create new level>" option. It's too unclear what will happen when you click it.

Michael Angeles noticed this as well. He sent me a storyboard of what he thought could be an improvement. (See attached file.) At first, I was very happy with this, because it made much more sense. However, "what in the case of enforce_deepest?", I thought. Because then you'd have to add another level, making it seem as if "enforce deepest level" isn't quite doing what it's supposed to do, *and* making it seem to work counter-intuitive. And finally, this could impact a lot of HS' internals quite deeply.
However, after thinking more about it, I decided that the current system for creating new levels was worse than the added counter-intuitiveness of an additional level. The benefits are too big.

So I just started making the changes. Turns out it's pretty darn easy to make this change! :) It only took me 15 minutes.

Thanks Michael. I really feel this was the final small push to make HS a truly solid product.