Volume command

[Dr-D3x73r]

Added Volume command from | Features to be added back #601

[galnir]

I'm about to push a new rewrite of the entire music system in the next day or two.
After lots of testing and researching into many libraries I've came to a conclusion that Lavalink is the way to go. It's much more stable in terms of music quality and has less errors which are everywhere in ytdl-core. Also the code is much cleaner :)
I'll leave this PR open incase I delay the new system

[galnir]

@MaximeLhortie I've merged the lava link pr branch, it has a new volume command
Thanks a lot for your commits tho, if you would like to help rewrite some of the features that need to be added back it would be great :) #667