set most members private and added getters

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

...c/main/java/com/xeiam/xchart/internal/chartpart/Axis.java

...in/java/com/xeiam/xchart/internal/chartpart/AxisPair.java

...in/java/com/xeiam/xchart/internal/chartpart/AxisTick.java

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

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

...n/java/com/xeiam/xchart/internal/chartpart/AxisTitle.java

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

...main/java/com/xeiam/xchart/internal/chartpart/Legend.java

...c/main/java/com/xeiam/xchart/internal/chartpart/Plot.java

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

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