Music Command Further Updates

[minhyungk]

Description of the new feature/enhancement

1. Change command format to subcommands, add configuration settings that allows the user to choose subcommands or not
//play => //music play

2. delete specific song in queue
   //queue delete 3
   deletes 3rd song in queue

3. Youtube playlist playing command
   //play "playlist url"
   plays the whole playlist

4. automatically suggest and play songs
   //play "keyword" auto
   automatically plays songs related to the keyword infinitely
   ex) //play "jazz" auto
   Closed by Autoplay2 #261

5. play desired song right away
   //play "keyword" -now

Proposed technical implementation details (optional)

subcommands: https://stackoverflow.com/questions/50548316/subcommands-in-python-bot