/tracks/replace events do not redraw the hierarchical track selector

[ihh]

The replaceTracks method for the hierarchical track selector is currently empty, meaning e.g. that if track names are changed on the server, the track selector is not updated.

This may have been due to the difficulties presented by the hierarchy being changed..? In any case the track selector should handle this with a robust fallback e.g. rebuilding the whole track selector view