Modified the playlist shuffling algorithm to avoid placing two instances of the same track next to each other. It checks the IDs of the tracks before and after the positions of the tracks that will be swapped, and if there's a match, it tries again with a new position.

It tries a maximum of 10 times, which should be far more than enough for normal situations. It uses the PlaylistTracks table in the database to get its track ID numbers. I didn't notice any significant performance decreases, even with hundreds of the same 10-15 tracks in the AutoDJ playlist.