They may not be, strictly, required at the moment, but as they're part
of how Antora organises content, it's good to have them tracked as early
as possible. See https://docs.antora.org/antora/1.1/component-structure/
for further details.
Antora implements a specific file and directory structure for
components, which you can find out more about at
https://docs.antora.org/antora/1.1/component-structure/. This commit
reorganises the existing images to follow that structure, as well as
optimises them, so that they're as small as possible, without losing any
quality.
