added bar thickness to style manager

...ain/java/com/xeiam/xchart/demo/charts/bar/BarChart06.java

xchart/src/main/java/com/xeiam/xchart/StyleManager.java

...xchart/internal/chartpart/AxisTickBarChartCalculator.java

.../xeiam/xchart/internal/chartpart/PlotContentBarChart.java

...xeiam/xchart/internal/chartpart/PlotContentLineChart.java

...in/java/com/xeiam/xchart/internal/style/GGPlot2Theme.java

...ain/java/com/xeiam/xchart/internal/style/MatlabTheme.java

.../src/main/java/com/xeiam/xchart/internal/style/Theme.java

...ain/java/com/xeiam/xchart/internal/style/XChartTheme.java