make data citeable

[michamos]

Data records need to be citeable. This means that:

• any Literature record that has a DOI in the references (references.reference.dois field) needs to have the matcher infer the data record ref in the corresponding field (references.record.$ref)
• data records need to have citation_count and citation_count_without_self_citations fields that are correctly computed based on citations and citations without self-citations as for literature
• refersto:recid:12345 search in literature should give all papers citing the record with recid 12345 also if it's a data record

[drjova]

@DonHaul this task is related to citations