setting the chartGroup should put the chart in that group

[gordonwoodhull]

As noted here:

http://stackoverflow.com/questions/27167079/dc-js-groupchart-example-with-dc-redraw

setting the chartGroup does not automatically put the chart in that group, and it's necessary to register the chart manually.

https://github.com/dc-js/dc.js/blob/master/src/base-mixin.js#L997

However, if the chartGroup is specified to the constructor, the constructor will call .anchor(), which will register the chart. It's doubly weird that another setter will update what the specific setter will not.