docs: recreate screenshots by PNG export

[nhoening]

(from #953)

Some pictures are not aligned very well and have artifacts, such as the cropped menu button and the visible cursor. Instead of manual screenshots, we could create these images using the PNG export button we have in the UI.

These two pictures would be good to recreate, as we show them together on the index page:

• https://raw.githubusercontent.com/FlexMeasures/screenshots/main/tut/toy-schedule/asset-view-without-solar.png
• https://raw.githubusercontent.com/FlexMeasures/screenshots/main/tut/toy-schedule/asset-view-with-solar.png

But there are more, e.g. https://raw.githubusercontent.com/FlexMeasures/screenshots/main/tut/toy-schedule/sensor-data-charging-with-solar.png

In essence, for this issue we should recreate all such pictures in our tutorials. This is ideal for someone running through them for the first time.

(technically, this might only require commits on the screenshot repo, but I still want the issue to be here)