Refactored Series click function:
 - Removed the unused element parameter.
 - Renamed filterFunc parameter since the expected argument is a crossfilter group object, not a function.
chartFilterHandler - rename argument to indicate that it is groupings that are filtered
Renamed ChartGroup.chartFilterHandler => filterByGrouping
Tidied ChartGroup tests
Reusing declared variable.
Simplified call to filterByGrouping
Tidying and simplification of ChartGroup tests
Removed duplicate Chart.seriesChanged function
Tidied ChartGroup tests and refactored filtering of a dimension to the Dimension class.
Partially completed clearFilters
Renamed highlight to toggleHighlight
Clearing highlighted chart and table elements when clearing filters.
Updated tests for ChartGroup.clearFilters
Using self.click as the click event handler in all series.
Update change log and docs
Removed unnecessary private mouseOver functions in series.
Re-added default ScatterSeries point opacity to 1.0
Removed unnecessary valueFunction parameter from Series.mouseOver
Update ChartGroup constructor tests naming
Merge pull request #184 from niksoper/feature/prog-filters

Programmatic ChartGroup filtering