Tom's ggplot2 themes

bar_graph.r

This file uses the ggplot2 theme_bw() as the baseline with the following changes:

1. Removes x axis ticks
2. Removes x axis major grid lines
3. Sets the panel border color to white
4. Makes the axes black

I also recommend removing the margin between the plot and the x-axis using `scale_y_continuous(expand = c(0,0))`.