Use virtual image loading

[ivmartel]

(not sure about the name...)
When loading a large number of images (either individually or in a multi-frame dataset), the viewer can reach the maximum allowed memory allocation of the browser. In Google Chrome this will result in the "Aw, snap" or "He's dead Jim!" out of memory error.
One solution could be to only load the images that are needed for visualisation and cache the others. For ideas, see the answers to this SO question: how-do-you-detect-memory-limits-in-javascript.

Originated from #255, relates to #249.

P.S. It seems 64bits versions of browsers are allowed more memory. I would recommend updating your browser if you are using the 32bits version.