[ticket/13034] Fix the route generated for the frontend not in the phpbb root

PHPBB3-13034
[ticket/13034] Fix unit tests

PHPBB3-13034
[ticket/13034] Use utf8_basename

PHPBB3-13034
[ticket/13034] Add comment

PHPBB3-13034
[ticket/13034] Update the base url to move to the root dir

PHPBB3-13034
[ticket/13034] Fix tests

PHPBB3-13034
Merge pull request #2921 from Nicofuma/ticket/13034

[ticket/13034] Fix the route generated for the frontend not in the phpbb root path