[ticket/7707] Add get_username_string() where possible

PHPBB3-7707
[ticket/7707] Remove unnecessary variables

PHPBB3-7707
[ticket/7707] Add get_username_string() once more

PHPBB3-7707
[ticket/7707] Remove unnecessary variables

PHPBB3-7707
[ticket/7707] Add comma to last entry of arrays

PHPBB3-7707
[ticket/7707] Fix undefined variable: perm_from

PHPBB3-7707
Merge remote-tracking branch 'Elsensee/ticket/7707' into develop-ascraeus

* Elsensee/ticket/7707:
  [ticket/7707] Fix undefined variable: perm_from
  [ticket/7707] Add comma to last entry of arrays
  [ticket/7707] Remove unnecessary variables
  [ticket/7707] Add get_username_string() once more
  [ticket/7707] Remove unnecessary variables
  [ticket/7707] Add get_username_string() where possible