move pie chart label drawing to function (to allow refresh on dataset delete)
code cleanup: better handling of dataset tracking
BugFix: refresh dataset index before label refresh and set color in label drawing function
use span instead of div, to prevent line break and clear label before redraw
BugFix: keep options in PieChartGui function
allow saving and loading of pie charts in LocalStorage
code cleanup: move user defined pie chart creation to function, as it is (or will be) used at multiple places
BugFix: move columnName to object (was a function parameter, which will be dismissed)
use (new) categorized pie chart creation instead (so a distinction between numeral and text based is not needed)
allow category rename and remove in category chooser
Merge branch 'origin/piechart'