Minor Functionality additions to Playlist creation/editing

[alphabitnz]

Just a couple of small things that would be good to have when creating or editing a playlist:

• Ability to Duplicate a selected playlist item (e.g. instead of having to go and re-create the specific Advanced Search used to add a Dynamic Selection, you could just clone the Playlist Item)

• Ability to 'Loop' a playlist so that it repeats within the timeslot instead of reverting to fallback media or black screen (useful for filler playlists etc)