when commentsfilter empty, do not show any comment

Closes #595

See merge request arsnova/frag.jetzt!538

# Conflicts:
#   src/app/components/shared/header/header.component.html

# Conflicts:
#   src/assets/i18n/creator/de.json
#   src/assets/i18n/creator/en.json

master

See merge request arsnova/frag.jetzt!531

This reverts commit a8c705b8.

staging

See merge request arsnova/frag.jetzt!530

This reverts commit a8c705b8.

Merge branch '542-questions-from-the-lecturer-or-moderator-should-always-be-displayed-first-no-matter-which-sort' into 'staging'

Show questions created by lecturer or moderator first, no matter which sorting is active

Closes #542

See merge request arsnova/frag.jetzt!529

592-staging-branch-should-deploy-to-staging-server

Closes #592

See merge request arsnova/frag.jetzt!527

This reverts commit a8c705b8.