use the new Package::fileUrl to load from resources
Summary: QUrl::fromLocalFile can't be used when packages are qrc
Test Plan: plasashell loads correctly with packages from qrc
Reviewers: Plasma, davidedmundson
Reviewed By: Plasma, davidedmundson
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D9176