Merge "Logo" styles

This changes remove extra `span` element.
Control "Logo" clickability more better

Using "Global Navigation"'s `margin-left` is better than `z-index`.
Remove non-layout styles from "Logo"

The color and shape of logo are defined in SVG logo image.
Include "Logo" into "Site Navigation"
Optimize "Global Main" top whitespace
Version 6.44.1