Refined-github: Default to rich diffs for SVG files

[fregante]

The feature existed but was broken. More info found in https://github.com/sindresorhus/refined-github/issues/2041

Removed in https://github.com/sindresorhus/refined-github/commit/e88a05df70ba76134a9b7e2331b18b999291927b, you can probably revert the commit and rewrite the loading behavior as suggested.

Originally asked in https://github.com/sindresorhus/refined-github/issues/1599

When SVG files are edited, usually the rich diff (rendered image) is more useful/desirable than textual diff.

This is particularly useful when such files are edited in an editor rather than by hand, since the changes are usually extensive enough to go over the size limit for showing the diff automatically, so neither the code nor the rich diff are shown by default (the "Load diff" link is shown instead). See for example pretty much any PR at icon repos, such as elementary/icons/pulls.

[SuperSandro2000]

I would like to see this for pictures.

[hex0cter]

+1, same request for other images.