Running VNC server for the headless display

We run our WebDriver tests in headless mode locally so that our other interactions with the machine don't screw up Firefox (it grabs focus, etc.). However, when running headless, we have no idea what the current test is doing.
This pull request adds a vnc support.

Usage:

Start the server via:
@headless.vnc.start

In your console, then connect to the vnc server via something similar to:
vncviewer localhost:5999