Create many-to-many tables for bibliography

[philiptzou]

There will be two many-to-many tables: article_variants, article_antibodies. Each table has following columns:

• ref_name
• var_name or ab_name
• article_type: enum('Animal model', 'Vaccine efficacy')

[KaimingTao]

Hmm, about article-related tables, can we also record both preprint and published papers, for future rechecking? About biorxiv, medrxiv papers, is it possible to add the version number?