Pie Chart improvements

...-demo/src/main/java/org/knowm/xchart/demo/XChartDemo.java

...ain/java/org/knowm/xchart/demo/charts/pie/PieChart01.java

...ain/java/org/knowm/xchart/demo/charts/pie/PieChart02.java

xchart/src/main/java/org/knowm/xchart/StyleManagerPie.java

.../java/org/knowm/xchart/internal/chartpart/ChartTitle.java

...main/java/org/knowm/xchart/internal/chartpart/Legend.java

.../org/knowm/xchart/internal/chartpart/LegendAxesChart.java

...n/java/org/knowm/xchart/internal/chartpart/LegendPie.java

.../org/knowm/xchart/internal/chartpart/PlotContent_Pie.java

...a/org/knowm/xchart/internal/chartpart/PlotContent_XY.java

...in/java/org/knowm/xchart/internal/style/GGPlot2Theme.java

...ain/java/org/knowm/xchart/internal/style/MatlabTheme.java

.../src/main/java/org/knowm/xchart/internal/style/Theme.java

...ain/java/org/knowm/xchart/internal/style/XChartTheme.java