When I upload an Image, the page should just refresh the images, not reload the whole thing

Summary: Currently, when I upload a photo, it hard-reloads the entire page in order to display that photo. That's crude: we should instead be refreshing just the relevant images on the page.

This borders on a usability bug, but isn't quite -- it's currently a bit inaesthetic and unpleasant, but works fine.

Fixing it probably requires marking each image with enough distinctive information to be able to figure out which is which -- probably the entire Property Path, including List index. The upload dialog box will need to be sensitive to exactly what it is replacing, and the client/server protocol should send back both the new filename and thumbnail filename to splice in. If we are adding instead of replacing, it should stuff the new thumbnail into the List in the right place. And once it has done all this, it should fade out the dialog.