Added bar diff, proportional graphs and labels

Previously, regardless of the amount of data in the graph data, the width of the container was split in equal parts.
With proportional width, the data is split proportionally to the total amount of data in each container.

Bar diff allows you to compare 2 set of data in a multi graph scenario.
Finally bar label, allows you to give each bar or (set of bar in a diff) a label, beyond the overall graph label