Pacem JS - <pacem-column-chart>

## Columns
`PacemColumnChartElement` (extensions of `PacemSeriesChartElement`) is a handy webcomponent that renders either **columns** and **stack** charts, it depends on the bindable `type` property.  
Its `PacemChartSeriesElement` children or its bindable `datasource` property define the groups of the chart.

> The `datasource` property **prevales** over the `PacemChartSeriesElement` children.

## Data-driven
The `datasource` property should be a consistent **2-dimensional datatable** having the following schema:

```typescript
type ChartDatasource = { 
    label: string,  
    values: { label: any /* label should consistently define the series name among all the datasource items */, value: number }[]
    color?:string, 
    className?:string }[];
```

The child-series of a chart can be easily updated by exploiting a `PacemRepeaterElement`. Everytime a change occurs
a **draw** task gets generated for the whole chart.

The following live examples sum up what can be done with a column chart webcomponent.