Send co-authors to CKAN as POST form lists

[HebaruSan]

Problem

See KSP-CKAN/NetKAN-Infra#293 and KSP-CKAN/NetKAN-Infra#294, the shared_authors property sent to CKAN just says username, so we can't use it to add the co-authors to pull requests.

Cause

435 was mis-guided; I thought the data sent to CKAN was in JSON format, but it's in POST form input format, which means it can only handle strings and lists of strings, not more complex data structures. That PR tried to send a list of dicts in the shared_authors property, which can't work.

Changes

• Now shared_authors is no longer sent
• Now Mod.all_authors provides the main author and all the co-authors for convenience
• Now these POST form inputs are lists with one element per (co-)author:
  • username
  • user_github
  • user_forum_id
  • user_forum_username
  • email
  • user_url (which was missed in #435 anyway)

On the CKAN side, request.form.get will return just the first element of the list, which ensures backwards compatibility, and request.form.getlist will return the entire list, which will allow a future update to get the data for all of the authors.

[HebaruSan]

The lists will all be the same length, see KSP-SpaceDock/SpaceDock#490. They're all generated from a list comprehension over the same list of authors.