Wavelink

Add `player.equalizer` property which allows the user to get the currently applied EQ.

Added `wavelink.WavelinkMixin` to be used in conjunction with a discord.py `commands.Cog`. This class allows for the registration of the new wavelink listeners:

`on_node_ready`
`on_track_start`
`on_track_end`
`on_track_stuck`
`on_track_exception`
`on_websocket_closed`

All listeners must be decorated with the `wavelink.WavelinkMixin.listener()` decorator.
All listeners must be in a `wavelink.WavelinkMixin` class.
Listeners can be stacked.

Docs
---------
[Event Payloads](https://wavelink.readthedocs.io/en/latest/wavelink.html#event-payloads)
[WavelinkMixin](https://wavelink.readthedocs.io/en/latest/wavelink.html#wavelinkmixin)

Example
-----------
py
class Music(commands.Cog, wavelink.WavelinkMixin):

wavelink.WavelinkMixin.listener()
async def on_node_ready(self, node):
print(f'Node {node.identifier} is ready!')

Change `websockets` to use `aiohttp`.
Remove `websockets` dependency.

Ensure `player.position` returns 0 at track start

Fix to `Client.__new__` returning false positives in `isinstance` check.
Checking is now done against `__qualname__`.

This major update fixes a bug which would keep old `on_socket_response` listeners alive when reinitialising the `wavelink.Client`, resulting in multiple `voice_state_updates` to be dispatched, causing a multitude of errors.

`wavalink.Client` has a breaking change, it now accepts a keyword only parameter `bot=` which is an instance of `commands.Bot` or `commands.AutoShardedBot`. Previously this was positional.