Simplify collision boxes #3

The collison box of stones is by default the same shape as the nodebox, not the selection box. When a player is walking across the top of a bunch of stones with the more complex collision box based on the node box, it causes some judder due to the player fitting into some small contours and "falling" a pixel or two before climbing back out. Making the collision boxes match the simpler selection boxes prevents this.

Thank you! I've manually done something similar, because there were merge conflicts, and it's a simple change. Will be included in my next commit.