BROOKLYN-12 Node.JS Entity

New entity implementing a Node.JS application. 
We should move the body of this into a common untility, something similar to `Networking.nextAvailablePort(int port)`. For example the code below:

    public static int firstAvailablePort(PortRange range) {
        for (Integer port : range) {
            if (Networking.isPortAvailable(port)) {
                return port;
            }
        }
        fail("someone is already listening on ports "+range+" on localhost");
    }

Unfortunately it can't go in `Networking` as `PortRange` isn't visible. We could consider moving PortRange and PortRanges into `brooklyn-utils-common`, next to `Networking`. But not in this PR.