Drag targets are now specified separately for each queuelike.

Drag targets are now specified separately for each queuelike.

Playlist rearrangement now implemented.

There's still a bug in playlist d+d handling somewhere, e.g.  make a
4-element playlist and rearrange the first three elements to after
themselves twice in a row.  The first time it succeeds (but using an
odd after_me) the second time it blows up.