[ticket/12369] Add template var {BODY_CLASS} to HTML body

http://tracker.phpbb.com/browse/PHPBB3-12369

PHPBB3-12369
[ticket/12369] Added ACP vars

PHPBB3-12369
[ticket/12369] Removed template vars initial state

PHPBB3-12369
[ticket/12369] White-space cleanup

PHPBB3-12369
Merge remote-tracking branch 'paybas/ticket/12369' into develop-ascraeus

* paybas/ticket/12369:
  [ticket/12369] White-space cleanup
  [ticket/12369] Removed template vars initial state
  [ticket/12369] Added ACP vars
  [ticket/12369] Add template var {BODY_CLASS} to HTML body