Fix score based sorting of sampled images in Image List

[PaulHax]

Problem

Currently, when a user sorts by an annotation similarity metric in the "Image List," only images that have been "processed" have a valid score and are correclty sorted. Images that have not scrolled into view don't get processed.

Also, show spinner for score, not 0 if not computed yet.

Approach

After processing images in view, system should continue processing the rest of the sampled images.

• Chaning the transform or inference model shall invalidate the scores and trigger reprocessing.
• Processed images shall be cached, until the cache is full so as not to eject "in view" images from cache.