spiralTileLoad loads tiles out of view

[bwoodall]

Having a small viewport but a large buffer with many overlays, the loading of tiles appears to be on and off since many of the tiles are loaded off of the viewport when you have a buffer => 2

So research a way to make spiralTileLoad load tiles that are in the viewport first and process the next layer(s) and then go back to load the remaining tiles that are in the buffer

[crschmidt]

dupe of #391.