Implements #356. This is based on #699 hence the extra commits / large diff unrelated to this change. This should clean up after (if?) #699 gets merged, but in the meantime, if you want to see what changed here, just look at the last commit.

I cleaned up the scaling settings UI because it doesn't make sense to me that someone would have the "Image scaling" setting checked but "Bilinear filtering" unchecked. The only use case I can think of for that combination is as a really terrible workaround for not having the ability to disable smooth scaling at high zoom levels, which this (obviously) now solves. I say terrible because the threshold at which "Image scaling" turns off is based on how far the image is zoomed in relative to the viewport size, rather than what I would call the true zoom level (relative to the image's original size).

I didn't make the threshold configurable in the UI; well I initially did but decided it looked bad, so went with a fixed value to keep things clean and simple. It goes through SettingsManager at least so someone could change it in the Registry or whatever if they really wanted.