Never delete z=0, z=1, even z=2 tile plots

[rafaqz]

There is still a small possibility of getting white flashes at the edges if you zoom out really fast after doing lots of scrolling around when zoomed in.

We could get around this and any other white flash problems by having some zoomed out tiles always sitting behind the other plots. At least you would see a blurry pixel of the right color instead of the obvious white flash. In the small flicker that its there for probably no one would notice how blurred it is. But the plain white background is really obvious.