Various fixes for series chart

Here are various improvements on the series chart - the most major change adding a preprocess step for coordinate grid charts so that it the series chart a chance to create the children before axes are calculated.

Also improved legend updates and removal of disappeared series (although this is really a hack, as compositeChart should have a way to remove a child).

And this defaults to using a crossfilter with a tuple-keyed dimension, and sorts the data accordingly.