Allow circular structures to be sent over the websocket, make it an error to send circular request bodies

[flotwig]

• Fixes Test runner hangs with RangeError: Maximum call stack size exceeded #4346
• Fixes Expecting element to be disabled results in maximum call stack size error #1958
• Upgrades socket.io from 1.7.4 to 2.2.0 so that custom parsers are supported
• Uses https://github.com/cypress-io/socket.io-circular-parser instead of Socket.io's default parser so that we can handle circular structures
• Adds a better error if a user passes a circular request body in
  • Even with circular JSON support in the socket, request lib can't serialize a recursive body (of course), so we should warn the user that they're sending an invalid body
  • 

Thought about using flatted (the successor to circular-json), but jsperf shows it performs 50% slower: https://jsperf.com/flatted-vs-circularjson

[brian-mann]

• use the global io instead of requiring in @packages/socket in the extension.
• build the extension to look at the source to ensure it's not packaging up socket.io twice
• we need to write a single "e2e / driver" test that passes in a circular dep.
• the test could be simple like something in cypress_spec.coffee or similar. we just need to use Cypress.backend(...) and pass in an object that would cause it to normally fail