Improvements to playListEntry

Summary:
enable playNow action when paused so that playback can be restarted from the playlist.

implement double click on the entry to start music playback.

change id to a more matching name

Reviewers: Elisa, mgallien

Reviewed By: Elisa, mgallien

Tags: Elisa

Differential Revision: https://phabricator.kde.org/D8393