Link back to parent site.
Remove register link and show 404 page if registrations are disabled.
Added custom fields to the Ticket Filters list.
Add a slug field to the Custom Fields table for use in the URL for ticket filters.
Added the `CustomField::get_ids()` method that returns an array of custom field IDs.
Custom field filters are now added to the URL.
Added form field for the custom field URL slug.
Fix upgrade file.
Merge remote-tracking branch 'main/master'