* Standardize author name cleanup across all import types
* Rename `authors_list` to `authors`; all return a list of authors
* Pubmed and HERO import fetch requests expect a list of integer values, not strings
* Pubmed and HERO ids returned in content are now integer instead of strings
* For HERO and RIS, don't save json field as string, but instead as JSON-compatible dictionary
* Python 3.6 or higher is required