Device playlists & two-way syncing

Thomas,

Here is my pull request for device playlists & two-way syncing. I incorporated your comments on my last commit, with the exception of the Windows-style line ending, as I think the Windows playlists will require enough tweaks (e.g. '\' for directories instead of '/') that I'll deal with them separately.

I'll send an email to the mailing list with more details.

Joseph