mulitiChart: fixes issues #328, #293 and partially #253

1. https://github.com/novus/nvd3/issues/328 fix -- show the y2 rules only if y1 has none (as in linePlusBarChart)
2. Allow to hide (by disabled) all series of lines and multibar chart type (https://github.com/novus/nvd3/issues/253 hide/show)
3. "nv-" prefix added to class names (https://github.com/novus/nvd3/issues/253 graph components)
4. Natural sub-charts ordering: stack, bars, lines (https://github.com/novus/nvd3/issues/293 and other related)