Consider incremental loading of images

[Michi Henning]

Suggestion from James:

628+}James Henstridge (jamesh) wrote on 2015-04-23:
It'd be useful to have a version here that could resize the image as it is being loaded, and perhaps one that can be fed incrementally (think reading a 10 megapixel JPEG with the intention of building a 100x100 pixel thumbnail).

Doing this would reduce memory requirements because we would scale directly from the source into the scaled pixbuf, rather than reading the entire image up-front only to pass it to the scaling function. It might be worth doing this as an optimization, especially when a gigantic image is turned into a small thumbnail.

[Michi Henning (michihenning)]

Fixed by James some time ago.