v2.3.3

Changelog:

• Show a "Set Assignment" link on gameboards teachers have already added, to save finding boards on the Set Assignments page.
• Add GCSE and Chemistry books to the My Progress page.
• Allow staff members to tag gameboards as "Created by Isaac".
• Don't show "Overdue" on completed assignments after their due date. Thanks to a Masterclass attendee for pointing this one out!
• Allow event attendance to be recorded in the events database. There is as yet no way of setting this information via the site.
• Fixes to event booking system and addition of waiting-list only events, and fix event email lists.
• Add a pull request checklist for contributors and feature branches to run through before adding new code.
• Prevent duplicate emails being sent by admin email code.
• Remove null values from database JSON records.
• Changes to Kafka config to prevent backfill issues, updates to site stats stream application. These changes require a Kafka restart and thus downtime.