Use Drupal filter formats to filter the HTML and overhaul the markdown logic

Ok, the problem was, that we escaped everything through the theme. This shouldn't be done. Instead, we should escape everything in PHP before passing it to Twig.

For project wiki contents everything will get escaped, except the body, which will get escaped, based on the filter format given in the WYSIWYG editor.

Now the markdown shows up escaped. Changing the markdown setting doesn't do anything.

Furthermore, we are currently escaping the content through the CommonMarkConverter. This is fine for pure PHP projects, but since Drupal also has these escaping capabilities, we should trust Drupal with the escaping and ditch the Commonmark validation.

All done.

Since, @Anybody is on holidays, and there is no proper release yet, I'll review this myself.

LGTM! Merged.

Automatically closed - issue fixed for 2 weeks with no activity.