WIP: 63 Use default header element and remove header component
Closes #63 (closed)
I added the Header element globally to App, but based on how the styling is supposed to look it can be added per screen.
There seems to be a margin at the top of the header that I can't get rid of. Likewise, the screen component seems to be overlapping slightly on top of the header - if we add a border around the header, we can see that it's visible except on the bottom.