Make use of discord.VoiceProtocol instead of socket_response

[PredaaA]

This PR makes use of discord.VoiceProtocol instead of listening to socket_response event. Which will be useful for next discord.py major release where that event no longer exists unless you pass a parameter to Client.
But it also makes things more "cleaner", as it "bind" the Red Lavalink Player object to discord.Guild object (guild.voice_client).
Though it comes with several breaking changes, that might break on current implementations of Red-Lavalink (in the case of Red's audio it doesn't seems to be a lot).

Breaking changes:

• player_manager.PlayerManager no longer exists. The needed methods are now in node.Node.
• Therefore Player.manager no longer exists too, node.Node can be accessed instead. Node.player_manager too.
• voice_ws_func parameter is no longer needed to be passed in node.Node, and therefore the get_voice_ws method has been removed too.
• player_manager.user_id & player_manager.channel_finder_func are removed.
• RESTClient now takes Player instead of Node as parameter.
• The rest_api.reset_session & rest_api.close methods are removed.

Fixes #98 & closes #97.

[Jackenmen]

It still make use of bot._connection._get_websocket though, maybe if there is an official API for that it would be better to use it

It seems we only use it here:
https://github.com/PredaaA/Red-Lavalink/blob/cff92370f2909f0796e662299c9e37cf46d71287/lavalink/player_manager.py#L246-L248

Which can probably be replaced with bot.is_closed().

[PredaaA]

It still make use of bot._connection._get_websocket though, maybe if there is an official API for that it would be better to use it

It seems we only use it here:
PredaaA/Red-Lavalink@cff9237/lavalink/player_manager.py#L246-L248

Which can probably be replaced with bot.is_closed().

I ended up using Shard.is_closed() instead, which seems to be doing the intended behavior (even on Red's cog side).
So the get_voice_ws method is removed too.

[FightMan01]

I'm testing this PR for 2 week now with my bot (9300+ guilds) and everything works fine. Thanks.

[PredaaA]

Sending that here so it won't be lost. There are mem leaks problems, and players state not being updated when stopped/disconnected.

[PredaaA]

Pushed changes from latest review that @aikaterna done and was pushed on another remote.

[PredaaA]

PR ready for review. (finally)

[aikaterna]

It should be 0.10.0

(nvm, I see what you're saying now Life)

[Jackenmen]

Superseded by #122