added scientific notation

src/com/xeiam/swing/SwingHelper.java

src/com/xeiam/xcharts/AxisTick.java

src/com/xeiam/xcharts/AxisTickLabels.java

src/com/xeiam/xcharts/example/SwingChart3.java

src/com/xeiam/xcharts/example/SwingChart4.java