Tiled browser interface

When visualizing extremely large image planes, it is necessary to load the plane in tiles, displaying only those portions that are currently visible, and caching tiles at several zoom levels, similar to [BrainMaps.org](http://brain-maps.org/) or Google Maps.

ImageJ 1.x provides a mechanism, the virtual stack, for handling very large datasets one image plane at a time. But there is no mechanism for working with image planes larger than 2 GPix (32-bit array indexing limit) and/or available memory—e.g., 40Kx40Kx16-bit = 2.98GB. ImgLib2 Cell images handle images planes of this size, but making it work in the legacy interface is another story.

Migrated-From: http://trac.imagej.net/ticket/43, http://trac.imagej.net/ticket/19

Begin with the tiled browser interface described in this issue and review how ImageJ 1.x virtual stacks and ImgLib2 Cell images relate to the legacy interface. Define tile visibility, multi-zoom caching, and support for image planes larger than 2 GPix; completion requires a working interface for such planes.

Written by the indexing model from the issue text.