Mainnavigation gets displayed on right side when used w/o metanavigation

[mfranzke]

When including a mainnavigation in header within a metanavigation, it will get displayed on the right hand side after one of our latest releases. To mitigate this for the moment we'll include some previous implementation parts again for the moment.

https://db-ui.github.io/elements/version/v0.22.0/?path=/story/02-navigation-header-intro--page
vs
https://db-ui.github.io/elements/version/v0.22.1/?path=/story/02-navigation-header-intro--page