Add header and footer to sidenav

[karolin-kivisikk]

In case the project doesn't need horizontal header sidenav should include heading and footer for logos, logout button, user name or settings etc.

With longer content header and footer should be fixed, or at least it should be adjustable from properties.

[ardokirsipuu]

The first iteration could be just to provide header and footer that take custom content as their inputs.

Quick demo of what is scrollable and what is sticky in our sidenav:

[karolin-kivisikk]

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