Add AV1 (*.avif file extension) image format support

[tobwz]

more and more pictures are published in AV1 Format (with *.avif extension). See here:

https://en.wikipedia.org/wiki/AVIF

I think it is becoming a very important, wide spread format in near future.

Unfortunately XnView is currently not able to show these images.
Can this add this format to XnView?

[xnview]

AVIF is supported by XnView MP