New functions CurrentURI, and CurrentURIMetaData

Use CurrentURI(), and CurrentURIMetaData() to get Info on CurrentURI and
MetaData.
Functions names corrected.
Added TrackURI(),TrackMetaData(); sorted(devices...)

TrackURI() and TrackMetaData() return the the URI and meta data of
current Track.
The list discover() outputs is now sorted by the names of the music
zones.