Make datatypes images to have a fixed size

[walkero-gr]

There are situations were the displayed image using datatypes is too big. Make it respect the screenshot size set on preferences.

https://eab.abime.net/showpost.php?p=1509026&postcount=208
https://eab.abime.net/showpost.php?p=1509028&postcount=209

[coldacid]

If we can resize the image via the datatype system, then we shouldn't need guigfx any longer. As far as I can tell, we're only using guigfx to handle the resizing of the image. However, guigfx does allow us to maintain the aspect ratio of the image for cases where the image aspect ratio and preferential screenshot size aspect ratio are different; we would need any datatypes-based resizing to respect the image aspect ratio.

[coldacid]

Looks like picture.datatype only supports image scaling from v45 onwards. Users of 3.9, 4.x, 3.1.4, and 3.2 will be able to get images scaled to a fixed size via datatypes, but users on 3.0, 3.1, and 3.5 would still need guigfx in order to keep the screenshot/icon images consistent. And this is even without aspect ratio in mind.