Plot target feature into time series preview as well

[louiskirsch]

No description provided.

[danthe96]

Value ranges can be very different, so we should think about rendering the target feature in a separate line chart or something similar.

[louiskirsch]

@danthe96 We might also just render it into the same plot and disable it by default, so the user can enable it to try whether the scaling makes sense.

But I am not sure whether this feature is of any use.