Gate.io integration

[minicheddar]

Add support for Gate.io cryptocurrency exchange:

• spot trades channel
  https://www.gate.io/docs/developers/apiv4/ws/en/#public-trades-channel

• spot orderbook channel
  https://www.gate.io/docs/developers/apiv4/ws/en/#order-book-channel

• perpetual futures trades channel
  https://www.gate.io/docs/developers/futures/ws/en/#trades-api

• perpetual futures orderbook channel
  https://www.gate.io/docs/developers/futures/ws/en/#order-book-api

[minicheddar]

completed spot trades + quotes, parking perps for later