Bar Charts

I needed a bar chart for my dashboard so I finished up the code for bar charts and made it work for data sets with multiple series.

I can provide a more indepth description of the changes if requested. The code renders the bars side by side (as opposed to stacked) and should work for a single series as well as multiple.

Let me know what you think. This is my first time working with d3 so I may not be following the best practices. More specifically, I'm not sure if using calculateX and calculateY is a d3 best practice but I wanted to wrap them in their own methods rather than using just x() and y() to allow for extension in the future. It should be fairly easy to modify these methods to allow stacked bar charts or other variants.

Thanks! - Austin