Make Stempelheft responsive (view users#show)

Make the overview of the stamps of a person responsive and more modern.

• plan the new design in figma
• remove the image in the background
• remove "Seiten löschen" and "zusätzliche leere Seite bitte" function
• edit the layout (grid)
• add image to the stempel units
• edit the css styling
• edit the process when pressing "ich nehme auch teil" button: The stamp is not placed on the overview side manually by the user but the unit of the stamp is automatically generated
• edit function when pressing "nehme doch nicht teil" button: stamp unit is automatically removed