[ticket/11972] Add posting_editor_subject_after template event

PHPBB3-11972
[ticket/11972] Add posting_editor_subject_before template event

PHPBB3-11972
[ticket/11972] Add posting_editor_message_before template event

PHPBB3-11972
[ticket/11972] Add posting_editor_message_after template event

PHPBB3-11972
[ticket/11972] Add the sinces

PHPBB3-11972
[ticket/11972] Fix the sinces

PHPBB3-11972
Merge pull request #1821 from imkingdavid/ticket/11972

[ticket/11972] Add template events to posting page