Authors metadata processing from CDS

[maria-grigorieva]

Currently stage 055_documents2ttl doesn't process 'authors' and
doesn't add author's metadata in TTL files.
Author's identification is a problem, because in the best case scenario we have

• INSPIRE number,
• CDS Number,
• affiliation,
• e-mail, and
• full name (first name and last name).

In worst scenario we may have only full name.
In this case we can't be sure that there are no authors with the same full name.

In Virtuoso we shouldn't store all authors for papers. But we must provide
access to the main authors, having INSPIRE number and CDS Control Number.