New template functions

Added the following template functions to retrieve metadata / check if
it exists withouth printing it.
- ids_get_acronym()
- ids_get_authors()
- ids_get_countries()
- ids_get_date_updated()
- ids_get_external_urls()
- ids_get_location_country()
- ids_get_organisation_type()
- ids_get_organisation_url()
- ids_get_regions()
- ids_get_themes()