[ticket/12808] Fix small gap between username and drop-down arrow

PHPBB3-12808
[ticket/12807] Changes PRUNE_FREQ to PRUNE_SHADOW_FREQ/_DAYS

PHPBB3-12807
[ticket/12807] Adds missing language variables language/en/acp/forums.php

PHPBB3-12807
[ticket/12807] New variables for _EXPLAIN

PHPBB3-12807
[ticket/12815] Show memberlist link for guests (if permitted)

PHPBB3-12815
[ticket/12815] Remove S_REGISTERED_USER for team link

PHPBB3-12815
Merge remote-tracking branch 'PayBas/ticket/12815' into develop-ascraeus

* PayBas/ticket/12815:
  [ticket/12815] Remove S_REGISTERED_USER for team link
  [ticket/12815] Show memberlist link for guests (if permitted)
Merge remote-tracking branch 'PayBas/ticket/12808' into develop-ascraeus

* PayBas/ticket/12808:
  [ticket/12808] Fix small gap between username and drop-down arrow
Merge remote-tracking branch 'Crizzo/ticket/12807' into develop-ascraeus