Neuroglancer image loading constantly breaks visual flow

[ceesem]

The way neuroglancer (including the original Google branch) loads images frequently disrupts the user's visual flow when navigating the volume, which makes following small processes significantly more difficult than it needs to be. This seems to occur both because central regions in the image view are not prioritized when downloading new chunks, and because it displays high mip levels first, even when the voxels are far too large to convey useful information. This can waste a lot of user time, and also require downloading a tremendous amount of data before any useful pixels appear up on the screen, so it would be an excellent area to try to improve.