[ticket/13023] Add template event posting_editor_buttons_custom_tags_before

PHPBB3-13023
Merge remote-tracking branch 'Nicofuma/ticket/13023' into develop-ascraeus

* Nicofuma/ticket/13023:
  [ticket/13023] Add template event posting_editor_buttons_custom_tags_before
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [ticket/13023] Add template event posting_editor_buttons_custom_tags_before

Conflicts:
	phpBB/styles/subsilver2/template/posting_buttons.html