Add field tooltip to ScatterSpot that is displayed as default

[DavidHuebner]

right now, the default tooltip when clicking on an element in a ScatterSpot is the radius as defined in the function

ScatterTooltipItem defaultScatterTooltipItem (ScatterSpot touchedSpot) { 
[...]
return ScatterTooltipItem('${touchedSpot.radius.toInt()}', textStyle, touchedSpot.radius + (touchedSpot.radius * 0.2));
}

I would find it more natural if the ScatterSpot class has an additional variable named String tooltip that is used for the tooltip and that radius is only used as a fallback if tooltip is not set.

[imaNNeo]

Do you want to change the text of the tooltip?
Check this #138, it may help you.