Update relation lines

This is the first of hopefully a few branches updating the look of the bundle visualizations.  This updates the styling of the relation lines to match that of the visualization used in the GUI.
Perhaps just call this strokeDashArray ?

Also, I think the calculation logic could be a little nicer here.
Something like this, perhaps?

	// strokeDashArray generates the stroke-dasharray attribute content so that
	// the relation health indicator is placed in an empty space.
	func (r *serviceRelation) strokeDashArray() string {
		return fmt.Sprintf("%g, 20", pointDistance(r.serviceA.point, r.serviceB.point))
	}
	
	// pointDistance returns the distance between the two points.
	func pointDistance(p1, p2 image.Point) float64 {
		dp := p2.Sub(p1)
		return math.Sqrt(square(float64(dp.X)) + square(float64(dp.Y)))
	}
	
	func square(x, y float64) float64 {
		return x * y
	}