Improve eleventy local images to save to IPFS

[bmann]

I forked to https://github.com/fission-suite/eleventy-plugin-local-images which is supposed to check if the file is already "local".

It uses a hashing function, so ideally we should make this "cache" to the IPFS version of this image, and replace file paths with either relative paths, OR with configurable gateway path.

Most time in build is spent fetching images. See:

This is probably a longer item, and in fact, improving / fixing the Ghost IPFS plugin we made so that full paths are on IPFS gateway would mean no copying if gateway detected.