Will make playlist window drag and drop to current selection (either media library or playlist).
This should make it somewhat more user friendly because it drops into where the user expects it to.

Fixes #4873
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
(cherry picked from commit 06c3e835dc0cd777d2fcf00e8cb68b68fc037d5d)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>