feat(#561): Update images in Play Store and App Store

We updated the screenshots in the Apple's App Store and Google's Play Store to give a more accurate impression what the users can expect when installing the app. 🤓

For this, we also applied some minor fixes here and there, for example, we added an option to create a sample library presenting some of the features the app supports as well as some improvements to the newly introduced menus of the app.

Closes #561 (closed)