Recommendation is to avoid using the year nomenclature as this
information is already encoded in the git repo. Avoids needing to
repeatly update.
Also updates AUTHORS.txt from current repo with contributor names
Break the non-PCB-specfic parts of PCB_REFERENCE_IMAGE out
to a common REFERENCE_IMAGE class, which is then composed into
the PCB_REFERENCE_IMAGE. This will make it easier to bring the
transform origin logic to eeschema without repetition.
Jeff Young