feat(websocket): Add serializer/deserializer config settings (#3489)

- Fixes the build for latest TypeScript
- Adds a `serializer` and `deserializer` config setting that defaults to JSON serialization both in and out of the socket
- deprecates the `resultSelector` (use `deserializer` instead)

BREAKING CHANGE: WebSocketSubject will now JSON serialize all messages sent over it by default, to return to the old behavior, pass a config setting of `serializer: x => x` like so: `websocket({ url, serializer: x => x })`

package.json

@@ -117,7 +117,7 @@
  "prepublish": "shx rm -rf ./typings && npm run build_all",
  "publish_docs": "./publish_docs.sh",
  "test_browser": "npm-run-all build_spec_browser && opn spec/support/mocha-browser-runner.html",
- "test": "cross-env TS_NODE_FAST=true mocha --require ts-node/register --opts spec-build/support/coverage.opts \"spec-build/**/*-spec.ts\"",
+ "test": "mocha --require ts-node/register --opts spec-build/support/coverage.opts \"spec-build/**/*-spec.ts\"",
  "test:cover": "cross-env TS_NODE_FAST=true nyc npm test",
  "test:circular": "dependency-cruise --validate .dependency-cruiser.json -x \"^node_modules\" src",
  "test:systemjs": "node integration/systemjs/systemjs-compatibility-spec.js",