fix issues related to radio and view details in playlist
Summary: partial removal of isRadio and duplicated code in TrackMetadataModel
Test Plan:
could not spot regressions
all automatic tests are OK except elisaqmltests that does not run due to an issue with a missing so dependency on KIO
Reviewers: Elisa, ngraham, jguidon, astippich
Reviewed By: Elisa, ngraham, astippich
Differential Revision: https://phabricator.kde.org/D23280