Iss1171 - Metadata entry

[EJMFarrow]

#1171

• UPDATES DATABASE with two new metadata fields for storing metadata JSON (one public, one private).
• Display creator and contributors on question edit page. Add button for main metadata entry modal.
• Add reactive form for entering metadata in modal.
• Allow direct editing of JSON and updating in both directions between input fields and JSON.
• Quick 'make me contributor/creator' buttons in modal.
• Add Behat tests.

This is now working across our supported Moodle versions and I've done some basic accessibility checks. Before I do another round of tests it's worth other people trying it out and deciding this is definitely what we want.