Subchart incompatible with intializing charts without "bindto"

I use the solution outlined in #382 to render multiple charts on one page.

When experimenting with adding a subchart, I noticed that these seem to be incompatible.

When using the `$('#id').append(chart.element);` method, the subchart renders, but the event listeners that bind to the brushes are not bound correctly. Switching to the `bindto` method makes the bug disappear.

Start by reviewing the approach described in #382 and reproducing the issue with multiple charts and a subchart. Compare initialization through $('#id').append(chart.element) with the bindto method, focusing on whether brush event listeners are bound correctly. Done means both initialization paths render the subchart and bind its brush events correctly.

Written by the indexing model from the issue text.