Make use of discord.VoiceProtocol instead of socket_response

[Drapersniper]

Supercedes #99 (Talked with @PredaaA who feels that making a new PR with theirs as a base would allow any changes requested to be more easily implemented by me, instead of me PRing changes to his branch)

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.
The rest_api.reset_session & rest_api.close methods are removed.
Fixes #98 & closes #97.

RESTClient now takes Player instead of Node as parameter.

• Player inherits RESTClient so no need to pass Node/Player to RESTClient

player_manager module renamed to player

lavalink.initialize() ws_port positional arg renamed to port

[Jackenmen]

• some of the references to PlayerState should be updated to refer to PositionTime now that it's been renamed (e.g. type hint of lavalink.lavalink._handle_update)
• DiscordVoiceSocketResponses enum is no longer used

[Jackenmen]

Thanks for the work @PredaaA, @Drapersniper, and @aikaterna!