Add playlists

[Xefise]

{user} - nullable. Default: this user. Looks like username#tag

Cmd list:

• s!playlist create {name}
• s!playlist remove playlist {name}
• s!playlist add music {music} {name} {user}
• s!playlist remove music {music} {name} {user}
• s!playlist info {name} {user}
• s!playlist list {user}
• s!playlist start {name} {user}

model:
{
id,
name,
author,
List musics
}