Don't put all images in a single folder

[jahands]

I've been hosting large maps and have found that storing 100k files in a single folder is not great - file systems aren't very good at that.

I've been using a custom version of the mod that uses Z/X/Y instead of Z_X_Y and have had noticeable improvement with moving them around.

It also makes it a lot easier to host them because I can easily cache the lower zoom levels while loading higher levels directly from object storage (b2). My script does this by listing the zoom levels for a save, which is just a few folders. Rather than having to list all files to figure out how many zoom levels there are (expensive). (Yes I could parse index.html but that's harder than listing subfolders in /Images/)