Bar graphs and pie charts

[JordanCheney]

Be able to make bar graphs and pie charts in addition to scatter plots. Skeleton functionality already exists in BarGraph and PieGraph classes. Awesome tutorial here-

http://www.raywenderlich.com/13269/how-to-draw-graphs-with-core-plot-part-1

and here

http://www.raywenderlich.com/13271/how-to-draw-graphs-with-core-plot-part-2

This could be a really good starting place for someone else to get some coding in.