Experimental automated testing

[rpl]

This pull request contains:

• "test/rdp-test-helper-jpext" submodule (needed to spawn instrumented firefox instances)
• "test/rdp-server.js" (needed to receive firefox instance connection and control the connected clients, e.g. exit the app)
• changes to "lib/browser.js" to integrate the RDPTestHelperActor
• "Gruntfile.js" (needed to automate the process)
• minor tweaks

[harthur]

Thanks for this, I'll take a look soon.