feat: 🍰 Header Menu To Component And Other Refinements

Created by: ogerly

🍰 Pullrequest

I have packed the header menu from the layout/default into a componente. on the layout/default maxMobileWidth: 811 is determined in a central position and showMobileMenu is passed through to the menu. the switching on and off of header mobil menu and footer is only controlled on the layout/default. i deleted all css that did that. so the default/layout is now very clear and we only have to change the value in one place if necessary.

Issue

relates #5545 (closed)