mimes: missing sizes

a few icon sizes are missing for:

- [x] image-x-xcf
- [x] authors
- [x] audio-x-playlist-rtl
- [x] text-x-generic-template-rtl

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- [ ] application-x-fictionbook+xml (128px)
- [x] text-x-ssa (16/24/32/128px)
- [x] extension (128px)
- [x] font-x-generic (16/24/128px)
- [ ] image-vnd.adobe.photoshop (16/24/128px)

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