[ticket/11885] Add migration files for 3.0.12-RC2 and RC3 and 3.0.12

PHPBB3-11885
[ticket/11885] Fix migration files for 3.0.12

PHPBB3-11885
[ticket/11885] Use conditional in update_data()

PHPBB3-11885
Merge pull request #1749 from imkingdavid/ticket/11885

[ticket/11885] Add migration files for 3.0.12-RC2 and RC3 and 3.0.12