[ticket/12438] Add Template event memberlist_view_content_prepend

PHPBB3-12438
Merge pull request #2346 from PayBas/ticket/12438

[ticket/12438] Add Template event memberlist_view_content_prepend

* PayBas/ticket/12438:
  [ticket/12438] Add Template event memberlist_view_content_prepend
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [ticket/12438] Add Template event memberlist_view_content_prepend