Please provide a default setup in the "ERT vis" plotter so that "ERT vis" immediately shows some plots

[KetilN]

Is your feature request related to a problem? Please describe.
A problem with getting users to start using the "ERT vis" plotter is that they do not normally see any data/plots with results immediately when starting up "ert vis".

Describe the solution you'd like
Please provide a default setup in the "ERT vis" plotter so that "ERT vis" immediately shows some plots presumably with data
(if this extra check also is possible).

Describe alternatives you've considered
Alternative is to show a big pop-up message to the user like:
"REMEMBER TO CHOOSE AN ENSEMBLE AND SOME RESPONSES BEFORE YOU CAN SEE ANY RESULTS".

Additional context
Here the problem-appearance with no data is shown upon start-up: