Loading progress indicator needed

[tyarkoni]

It would be good to add a progress bar when loading images; at the moment large images can take a while to load (particularly when read from binary file), and the user may wonder whether anything's happening.

[njvack]

Hm... if you're getting the data via XMLHttpRequest, it looks like there's a fairly simple way to hook into download progress:

https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/Using_XMLHttpRequest#Monitoring_progress