Resolve "A_019 Navigation menu refactor | Step 1: Header and top navigation spacing"

So after talking to Katrin, the following things were adjusted:

margin below the welcome text is now 24px.

If the screen width is (unrealistically) too narrow, the text will expand beyond the max-height of 72px into the margin below

The header-bar gets 24px padding top and bottom below the logo / icon

Closes #1265 (closed)