feat(graphiql-ws): add websocket support to graphiql

[DxCx]

Hi @helfer
I've added web-socket support to graphiql (Running the new proposed WS protocol)
please start with reviewing process, i'll merge after the whole ws integration suite will be ready for merge.

TODO:

• Update CHANGELOG.md with your change (include reference to issue & this PR)
• Make sure all of the significant new logic is covered by tests
• Rebase your changes on master so that they can be merged easily
• Make sure all tests and linter rules pass

Closes #222
Related to #272

[helfer]

This is pretty neat @DxCx! I like how simple the websocket fetcher is. The code should in my opinion be refactored a bit to make it easier to read. The ternary operators with long strings between them are not very legible.
Apart from changing the message format to match the protocol we end up deciding on, I think everything else looks pretty good. We should continue the discussion about the diff format in the other thread.

I'm not a fan of including all of RxJs, but since it's a developer tool the initial startup time probably isn't critical.

[DxCx]

@helfer im planning in the future to replace this code with one that takes the apollo-client's network interface and use it instead.
because of that i approved myself use RxJs in the time being as the client side is not ready yet.

[DxCx]

Replaced by #308