State updates for web UI

• Separate websocket implementation into trait
  • This should allow the web version to work without being forced to use tokio or actix.
  • Also moved client connection specifics into CLI because web version will use different methods to send HTTP requests.
• Only create song player when we are playing. This allows remote TUI instances when no audio device exists.
• Make all operations on PlayerStateManager work with immutable borrow.
  • This allows it to be held in an Arc and not need external locking.