[ticket/9657] Fix variable naming of phpEx to php_ext

PHPBB3-9657
[ticket/9657] Initialise variable outside of the loop

PHPBB3-9657
[ticket/9657] Use include instead of include_once

PHPBB3-9657
[ticket/9657] Remove sql_visibility as it is always non-empty

PHPBB3-9657
[ticket/9657] Add type hints for classes

PHPBB3-9657
[ticket/9657] Notifications do not require emails or jabber anymore

PHPBB3-9657
[ticket/9657] Fix english language :(

PHPBB3-9657