add support for resource listings: playlists, shows, snapshots, cues #85
Description
related to discussion in #78
Retrieving information about playlists, shows, snapshots and cues is not trivial since it's not part of the global mixer state.
Instead, this info is sent on request per client.
Therefore, we need a proper design for this different kind of interaction.
Example
Request playlists
MEDIA_GET_PLISTS
mixer replies with
PLISTS^Recordings