[ticket/12273] Allow to filter events for extensions

PHPBB3-12273
[ticket/12273] Update exporter to allow specifying an extension

PHPBB3-12273
[ticket/12273] Fix return description

PHPBB3-12273
[ticket/12273] Do not allow template events in non-html files

PHPBB3-12273
[ticket/12273] Also check file for adm "Location:" events

PHPBB3-12273