New function xAxisLegendEvery with autodetect

[ddTech]

When using longer time series or data points along the x axis, the labels can become unreadable even when placed at an angle, simply because the lables need more space than available.

Therefore I added a new functionality which allows to omit labels. Instead of "Jan, Feb, Mar, Apr,..." "Jan, Mar..." or "Jan, Apr, ..." will be printed depending on the setting of xAxisLegendEvery (xAxisLabelEvery would actually be the better name). If this value is set to -1 the iteration will be detected automatically based on the value of xAxisLegendEverySpacing. This is the preferred setting as it automatically recalculates when the chart is being resized and the labels always remain readable.

There is a third property xAxisLegendEveryOffset which allows the iteration to shift (i.e. start with a certain month).

Regards

Frank