Update all: sort by download size, ascending

The Update all button processes the apps in alphabetical order. This makes Fennec and Element/SchildiChat block the queue.

My Internet connection makes a small download take almost as long as app installation. So I manually download the smallest apps first, install as soon as they are ready and overlap installation with the next downloads. By the time the smaller apps are finished installing, the largest apps are finished downloading. This is more efficient than prioritizing according to the app name.