Remove last TODO comment (Done)
Add CSS class to each chart based on grouping name

The CSS class is built by replacing the suffix '-categories'
in the grouping name with '-chart'.

At this point, all the charts in a grouping get the same CSS class;
an extra class could be specified in layout configuration to apply
different styles to individual charts.
Display only 1 SVG chart per row for a selected set of charts

The selection is made through CSS selectors in style/charts.css,
by applying the CSS style display: block.
Merge branch 'enhancements'
Merge branch 'master' into gh-pages