This is a lot of smaller changes and fixes that were requested over the past academic year.

Features

Add archiving to roles: this creates a new role with all users on a specific role, and then clears the old role of users.
Add purging to roles: this removes all users from a role.
Mass add techies to the tree.
Add test emailer.
Add select field for the author on an event which is populated with all current authors on the website to increase uniformity.

Changes

Add state field to proposals to keep track of whether it was approved and successful, rather than relying on two booleans.
Only admins can now add users to role: otherwise, any user that can edit users can add users to roles, which means they can make themselves admin, which is unwanted.
Never display workshops in the main carousel
Reorder questionnaires by end date of the show rather than by id of the questionnaire, which was oddly unchronological.
Remove the redundant markdown explanation to the side of question fields, and add one overview at the top of the page instead.
Book now card on the home page now has an editable block.
Email addressee is now "Name Name \<email>" instead of "email".
Show most recent maintenance session at the top by default.
Admins no longer can add non-members by default to avoid cluttering the select field. They can give themselves the permission to re-enable.

Fix issue with a babel dependency preventing webpacker from compiling
Display correct maintenance attendance count
Add_non_members permission works again.
Fix errors when ransacking based on tags due to a ransackable_associations misconfiguration.