Faster dc.filterAll()

[ehansis]

Fixes #1322

[gordonwoodhull]

This looks good to me, but why is it necessary to call .filter(0) on all of those charts in the tests?

[ehansis]

In charts w/ grouping, the tests check that chart.filterAll() is called or not called on a chart depending on its chart group. Since the modified dc.filterAll() only calls chart.filterAll() on charts that have a filter set, we need to set a filter on each chart to do a meaningful test.