Add sample using Datalabels plugin

[stockiNail]

Fix #75

EDIT: sets karma-rollup-preprocessor to version 7.0.7 to avoid usual bugs on that.

[stockiNail]

@kurkle tought: due to the datalabels plugin sounds working with treemap controller, do you think it still makes sense to have labels and captions capabilities in the controller? Maybe they could be delegated to data-labels.

[kurkle]

@stockiNail about dataLabels, yes it would be best to rely on that plugin for the labels, it would avoid a lot of code.

[stockiNail]

@stockiNail about dataLabels, yes it would be best to rely on that plugin for the labels, it would avoid a lot of code.

I thought more on that. for Labels could be a good idea even if we couldn't address some enhancement (see #92). The caption could be manage by datalabels because needs to add space for that to the element and we need options that, going to datalabels, could be managed only by plugin. Therefore some login on labels for caption will remain.