Add 'karaoke' mode

[tgoins]

Add a 'karaoke' mode which, once enabled, when the user searched a song, it will return the karaoke version of the song if it exists. If the result isn't the karaoke version, try finding an instrumental of the song, and if that doesn't work, then tell the user the karaoke version could not be found.

If the user inputs a link, then use the link to get the video title, check if it is either an instrumental or karaoke version of the song, or find the karaoke version or instrumental of the song, or tell the user that the instrumental can't be found.

Add 'karaokeModeEnabled' to the config, and add a 'karaoke' command to set the config variable.