[musicdb] cosmetic: change to using XMLUtils for the album XML getters/setters
[musicdb] cosmetic: artist.cpp XML cosmetics
[musicdb] cosmetic: rename song.iAlbumId to song.idAlbum
[musicdb] cosmetic: restructured MusicDatabase.h to be a bit clearer and add some comments
[musicdb] fix: 'include artists who appear only on compilations: off' didn't work
[musicdb] fix: restructure the filecountreader so it can be killed and kill the thread before modifying shared variables