[WIP] xdg thumbnails fetching with fallback on mimetype icons #499

Job	Run time
build-autotools-gcc	2m 56s
build-meson-clang	1m 32s
build-autotools-clang	3m 19s
build-meson-gcc	1m 28s
build-autotools-gcc-no-window	3m 6s
	12m 21s

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