Fixed decimal number format.

Transform to string decimal and double arrays using
CultureInfo.InvariantCulture in order to not use comma in some
locales when preparing the javascript code.

This fixes cases where the output javascript is generated from
a Series of data made of a double[] on locales with comma
as decimal separator the generated javascript code uses
comma as decimal separator, which is wrong and will yield
to wrong results: eg: [0,2394 , 0,24932] instead of [0.2394 , 0.24932].
Differently with locales like USA this works correctly.
Fix backgroundColor and plotBackGround color format.

These two properties are correctly handled when using gradients,
but in case case code like the next block is used, which uses
a plain color the output will be like this backgroundColor : { '#123456' },
which is wrong as HighChart expects it to be like backgroundColor : '#123456'.

chart.InitChart(
new Chart { DefaultSeriesType = ChartTypes.Area,
PlotBackgroundColor = new BackColorOrGradient(Color.Gray) });

This is the format which can be seen on samples provided by HighChart on
http://jsfiddle.net/gh/get/jquery/1.7.2/highslide-software/highcharts.com/tree/master/samples/highcharts/chart/plotbackgroundcolor-color/ and
http://jsfiddle.net/gh/get/jquery/1.7.2/highslide-software/highcharts.com/tree/master/samples/highcharts/chart/plotbackgroundcolor-gradient/
Added new chart types: Arearange, Areasplinerange, Columnrange.

As of Highchart 2.3 there are some new chart types:
arearange, areasplinerange and columnrange.

This adds the types to the chart type enum and allows to declare them as
the type, but doesn't provide options specific to them.