Sort the source list in lexicographic order

[8jmm3]

I am using mpd as my back-end media player. It currently supplies a list of playlists as sources in a seemingly arbitrary order (map order). This makes choosing a source from the UI drop down quite cumbersome since they are in no obvious order (e.g. Rock, Pop, Alternative, Jazz, Classical). This is even more apparent since I have over 20 playlists.

This change implements lexicographic sorting of the source list so that the choices appear in a more logical order. (e.g. Alternative, Classical, Jazz, Pop, Rock).