Consistency tweaks in Global nav

[fcoveram]

As proposed in #535, the design introduced involves changes in both local and global nav. For the latter, the changes are general spacings to reach consistency across the two components, and on mobile, the menu has new text styles that make group indentation clearer.

Here is an image of global nav menu in both desktop and mobile views.

Here is an image of the main components of Global Nav.

---

All changes are documented in the Design page of "Simpler navigation" file.