v5 custom header and footer layout bugs

creating a custom header / footer breaks few things a bit 🤔

1) if you have very short page, there will be always a vertical scrollbar, because it doesnt count with extra space for custom header and footer

2) if you use custom header and footer, it makes the mobile menu position incorrect - it should be always fixed to top / bottom, even with custom header / footer (i guess)

this could be easily fixed by moving custom header / footer from "after opening and before closing body tag" to "before standard header and after standard footer" 🤔