Change captains to allow multiple players

[slmnio]

At the moment, captains can only be a single player - both on the database and the website. However, we've been running more and more events where teams are run by 2 captains from the start - usually a playing captain and managing captain. Until now, we've usually set the playing captain as the Captain and the managing captain as a member of Team Staff.

To improve:

• [x] Update Airtable to allow multiple player records in captain fields
• [x] Update team pages to show captain(s) as an array
• [x] Confirm that player pages still work (they should) with the change

[slmnio]

Can also do this with the owner attribute while we're at it