Convert 4 of the biggest video to webm.

[Carreau]

Remove equivalent Gifs.

This should massively reduce the size of the data transfer for some of the video, sometime 10x or more.

I haven't changed all, as I was not able to properly build locally, so I was not able to try it, I'm not sure if the image tag works with webm.

One drawback is that we may not have auto looping, and may get video control depending on the browsers.

[Carreau]

Love this! I didn't know you could do webm using a standard image tag!

Yeah it's "fairly new", and that's why I said I haven't tested. I thought there might be some preview pages as I couldn't build locally. But I'll retry.

[psobolewskiPhD]

Looks like these changes are live, e.g. https://napari.org/stable/tutorials/processing/dask.html#processing-data-with-dask-array-map-blocks