Editing track unique ID prefixes

[mzgajner]

Tracks are currently marked with an internally standardised unique ID (e.g. LPYU 123456-B/00). The prefixes (LPYU in this case) have corresponding real life shelves in the music library and represent an important part of the categorisation system.

These prefixes will probably be hard coded initially, but It would be useful to make them customizable at some point so that the manager of the music library can add new sections if required.