composite child charts do not fire pre/post redraw/render events

[gordonwoodhull]

1. The composite chart calls child.plotData() for children (and not ._doRender or ._doRedraw`)
2. The composite chart calls child._activateRenderlets() - with no argument, this does not fire postRender or postRedraw

This is probably an oversight. These are useful: we should add them.

In the meantime, it looks like pretransition and renderlet events do fire okay for child charts.

[gordonwoodhull]

In addition, the renderlet event does not fire because it is attached to the svg element, which is shared between the composite and its children.

Attaching it to the g element with (_chart.g ? _chart.g() : _svg).transition() works but is pretty nasty.