new feaure - for bar charts with more than 12 categories, the axis labels get pruned

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

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

...m/xeiam/xchart/internal/chartpart/AxisTickCalculator.java

...iam/xchart/internal/chartpart/AxisTickDateCalculator.java

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

...art/internal/chartpart/AxisTickLogarithmicCalculator.java

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

...chart/internal/chartpart/AxisTickNumericalCalculator.java

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

...est/java/com/xeiam/xchart/DateAxisTickCalculatorTest.java

.../java/com/xeiam/xchart/DecimalAxisTickCalculatorTest.java