[ticket/12473] Move compatibility globals out into its own file.

PHPBB3-12473
[ticket/12473] Add more compatibility to phpBB Console Application.

PHPBB3-12473
[ticket/12473] Add console command for database migration.

PHPBB3-12473
Merge remote-tracking branch 'github-bantu/ticket/12473' into develop-ascraeus

* github-bantu/ticket/12473:
  [ticket/12473] Add console command for database migration.
  [ticket/12473] Add more compatibility to phpBB Console Application.
  [ticket/12473] Move compatibility globals out into its own file.