Improve DCAT and Dublin Core mappings

[samueljackson92]

This is a placeholder issue for improving the DCAT and Dublin Core mappings for FAIR MAST.

@agbeltran you have mentioned that you have noticed some improvements that should be made. Perhaps can you document them here and we can fix/improve things?

[samueljackson92]

@LariDG may be of interest to you.