Romain Vimont authored Oct 15, 2018 and Thomas Guillem committed Nov 15, 2018

Add a new playlist API.

A playlist contains a simple list of items, and owns a player.

Callbacks are exposed so that clients (UI) are notified when items are
updated, insert, moved or removed. The playlist is responsible for the
playback order and repeat mode, and manages a cursor to the "current"
item.

Signed-off-by: Thomas Guillem <thomas@gllm.fr>