Overhaul admin interface

[multimeric]

PR Checklist

• This comment contains a description of changes (with reason)
• Referenced issue is linked
• If you've fixed a bug or added code that should be tested, add tests!
• Documentation in docs is updated
• docs/changelog.md is updated

Description of changes

• Allow unprivileged users to create new filters and delete their own filters via the REST API. This also resolves issues where these users couldn't create their own filters on certain pages.
• Give all users access to the admin interface. Unprivileged users won't be able to edit or delete most entities, however
• Added a "Filters" resource to the admin interface, allowing users to view, edit and delete filters there. This closes Cannot delete filters from 'Edit Filters' tab #476
• Consistently added show, edit and delete buttons to all pages of the admin interface

Technical details

Additional context