artist, album artist, genre composer and lyricist can be strings list: fix Elisa

Summary: artist, album artist, genre composer and lyricist can be strings list: fix Elisa

Test Plan: tests are OK and more metadata are recognised by Elisa

Reviewers: Elisa, astippich

Reviewed By: Elisa, astippich

Subscribers: astippich

Differential Revision: https://phabricator.kde.org/D11340