Bubbleupnp's work display behavior - suitable minimserver tagging

[simoncn]

For showing the movements of a piano quartet (etc.) grouped together as a single item when browsing, you need to use the Group tag. If you want to browse your library by musical work name, you should use the Work tag.

The Group and Work tags will often be the same but in some cases they will not (for example, when a work has only a single movement).