Converted grouped column chart to a plugin
Renamed line-chart style.css to line-chart.css
Renamed bar chart style.css to bar-chart.css
Merge branch 'plugins' of github.com:datawrapper/datawrapper into plugins
Merge branch 'plugins' of github.com:datawrapper/datawrapper into plugins
Made visualization-line-chart plugin inherit from visualization-raphael-chart