* Scale: added the stacked property for all scales
* interfaces: generic type LABEL can be string, Date, etc.
* controllers: stack can be used for all types of dataset
* docs/data-structures: added general dataset properties
Co-authored-by: Sergey Khomushin <sergey@placer.io>
* Rename elements to mark as elements, i.e. Arc -> ArcElement
* Rename RectangleElement to BarElement
* Also updates options.elements.rectangle to options.elements.bar