Add webpack plugin for metadata generation

[andersevenrud]

Would be nice to have a way to scan the webpack bundling results and place the source files (mainly .js and .css) into the metadata.json file automatically.

This needs a separate repo, and then be added to this meta package.

[andersevenrud]

Even better, if there could be a way to replace any proc.resource('filename') resource with anything that went out of the bundle, that would be awesome.