Adding nested dashboards

src/css/widget-theme.scss

src/js/charts/areachart.js

src/js/charts/barchart.js

src/js/charts/base.js

src/js/charts/linechart.js

src/js/charts/piechart.js

src/js/charts/stacked_barchart.js

src/js/main.js

src/js/utils.js