Fix emptyContent once more

[jotoeri]

• Now went back to the action slot, so action and description can be properly formatted here on the component.
• The description also became a prop, thus beeing consistent with the title.
• Adapting resp. docs
• Adapting Usage within DashboardWidget

I considered alternatively to make the old description slot a flex-element for centering items, that however didn't allow me to put some margin between text and action here on the component. So apps would have needed to separately style the distance between.

Before	After

[skjnldsv]

Sure! 👍

[raimund-schluessler]

Why not.