[ticket/13133] Allow @vendor_name for includecss

PHPBB3-13133
[ticket/13133] Add unit tests

PHPBB3-13133
[ticket/13133] Rename $ok variable

PHPBB3-13133
Merge pull request #3023 from Nicofuma/ticket/13133

[ticket/13133] Allow @vendor_name for includecss
Merge branch 'develop-ascraeus' into develop