Implement playlists logic

[jellegerbrandy]

This needs to be defined, still. Here is a first idea:

 `paratii.core.playlists.get(playlistId)`
 `paratii.core.playlists.create(...)`
 `paratii.core.playlists.update(playlistId, {fiedls:to, update:foo})`
 `paratii.core.playlists.search(qry)`

Gettings videos of a playlist:

 `paratii.core.vids.search({ playlist: playlistId })`

Get playlist of a video:

  `paratii.core.playlists.search( { video: videoId })`

[jellegerbrandy]

This issue needs some more speccing...