working space int to double precision

...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

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

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