Fauxton: make hidden tabs in _changes visible

I found some hidden tabs in the `_changes`-screen I am working on, they are positioned behind the upper header with the breadcrumbs.

I am not sure if we want them, but I made them visible so everybody can have a look.

I find the tabs very useful, but maybe they should be positioned `fixed` so it's always in the screen and not just on scrolldown.

**Merge with caution**: if it is planned that e.g. `Config` will get a fixed header like most views, the padding for tabs makes sense. If not and there would be tabs added, the tabs would have too much space to the top.

- Should we keep the tabs?
- Will all screens get this fixed header?