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.
Updated Markdown plugin to use the PHP Markdown Extra library.
Added the `get_slugs()` method to the `CustomField` model.
Added the `ticket_filters_for($project)` helper.
Started adding support for custom fields to the ticket filter SQL query helper.
Removing of a ticket filter is now done via JavaScript and does not auto-submit the form.
All ticket filters can now be removed.
Changed the ticket filter help functions to return both the URL string and name of the filter.
Add copyright and package to the `ticket_filters_for()` helper.
Custom field filters working.
The ticket filters form visibility can now be toggled.
Merge remote-tracking branch 'main/master' into i18n