Improve accessibility with more visible focus indication for non vue apps

Improve accessibility with more visible focus indication for non vue apps

- Add visible-focus effect on each header entry
- Show focus outline when using focus-visible (keyboard navigation)
- Add polyfy for focus-visible since it's only very recently available
  on webkit
- Change text for link to home button to describe the destination and
  not the current page
- Improve focus effect in app sidebar navigation

Signed-off-by: Carl Schwan <carl@carlschwan.eu>