misc cleanup

...n/java/com/xeiam/xchart/demo/charts/line/LineChart04.java

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

...a/com/xeiam/xchart/internal/chartpart/AxisTickLabels.java

...va/com/xeiam/xchart/internal/chartpart/AxisTickMarks.java

...ava/com/xeiam/xchart/internal/chartpart/ChartPainter.java

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

...java/com/xeiam/xchart/internal/chartpart/PlotSurface.java