Omit chart if all values are zero

[senier]

Do not show a chart if all values of the data series(es) are zero. Optionally, print a text in place of the chart.

This makes the UI clearer if certain features are not being used (like RPE).

Don't hesitate to request (or make) changes if you think this should be solved differently!

[treiher]

At first I was a bit worried that omitting diagrams might be confusing in some cases, but I agree that the user interface is clearer when unused diagrams are omitted. I think this is a good improvement.

[senier]

@treiher I applied the suggested changes and also fixed some complaints that clippy had.

Do you know what the issue with the frontend checks is? This happens to me on main, too, and doesn't seem to be related to my changes.

[treiher]

The failing end-to-end tests were caused by an update of Chromium. Unfortunately, I couldn't find a solution for these issues, so I had to disable the affected test parts (see #56 and #57). All checks on main are successful now.

[senier]

The failing end-to-end tests were caused by an update of Chromium. Unfortunately, I couldn't find a solution for these issues, so I had to disable the affected test parts (see #56 and #57). All checks on main are successful now.

That's annoying! Thanks for looking into that issue. The tests succeed for me now, too.