[ticket/12516] Always preview signature in UCP/ACP module

PHPBB3-12516
Merge pull request #2557 from Elsensee/ticket/12516

[ticket/12516] Always preview signature in UCP/ACP module

* Elsensee/ticket/12516:
  [ticket/12516] Always preview signature in UCP/ACP module
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [ticket/12516] Always preview signature in UCP/ACP module