simplify order's signature

This simplifies the comparison functions that the caller has to pass in when ordering.  Previously you'd have to pass in something like:

    g.V.order({arg: TPair[String, String] =>
      arg.getB.compareTo(arg.getA).asInstanceOf[JInteger]
    })

This change allows you to drop the `asInstanceOf[JInteger]`:

    g.V.order({arg: TPair[String, String] =>
      arg.getB.compareTo(arg.getA)
    })