Display of Multiple Artists of FLAC Music Files

Since Volumio already provides support for organizing music files according to all tagged artists and/or album artists, the user interface in the library view and play list view should also be able to display the all the artists tagged in each FLAC music file. Currently only the first artist is shown. On the other hand, a MPD console client ncmpcpp and an iOS app Flacbox are able to display all the artists associated with each file. This is an easy fix for the front end of Volumio.