Feature: (de-)selectable lines

[brasilikum]

Why?
Being able to select only a subset of datapoints you want to look at in combination with automatic scaling of the y axis makes it possible to explore differences between datapoints that are very close together in comparison to other points you are not interested in.

How?
Clicking on a legend item could only select the line belonging to it.
Clicking again could deselect it.
Deselecting all items would equal selecting all items.

I am fascinated by the clarity in terms of user experience and visual representation of this package. @terezka do you think this feature can be added without compromizing on the design goals?