add y sort property

[cromerc]

This allows Y sorting to be turned on or off as a property. This is important because large tile maps of the size 512x512 for example create 262,144 objects and reserve memory for them while running and then it has to sort them constantly by their Y coordinates as they are drawn each frame.

With a map size of 512x512 I was getting around 10 FPS. After turning off y sorting on that map which I didn't need Y sorting at all, I am now sitting at 60 FPS running smoothly.