Add Autobahn echo server with Dockerfile

[djones6]

While testing Kitura-WebSocket, I wanted to run the Autobahn tests against my changes. The existing guide in AutobahnTests.md is helpful, but it's a pain to have to install all the dependencies for the client, deal with versions of Python, missing macOS headers and so on.

I found that there's an autobahn docker image (https://github.com/crossbario/autobahn-testsuite/tree/master/docker) that we can use for the client. And we can do everything within Docker if we dockerize the echo server and run both on a network.

To that end, I've created an Autobahn subproject containing a Dockerfile and a run.sh which wil build the server into a wsserver image, run that as a container on a Docker network called autobahn, and then run the autobahn client (on the same network) targetting wsserver:9001. At the end of the run, it'll open the HTML report that the client generates.

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