Reconsider the mouse button labels

[codeZeilen]

E.g. from #68

• G1. yellow / blue / red clicking I am not sure if I might be touching on some treasured conventions here, but I think readability for beginners would be improved by referring to yellow, red and blue clicking by left, right and "option" clicking. image not everyone has a mouse like that :D

The colors are very much confusing for beginners (ironically). While the mapping might depend on the OS, most users are aware that there is a button to select things, a button for opening context menus, and a button for "meta" actions.

[LinqLover]

In Squeak, I have always deemed it a best practice to only reference the mouse buttons by their color. So, while we might deviate from this practice in the book, we should still introduce the color names so that any other help texts/instructions in the image and additional documentation remain understandable for new beginners.