=doc New styling and logos for the documentation

* Updated CSS Styles, new logos (SVG format), New header/nav design. General colors overrides, small but safe HTML changes, new favicon.
* Updated GA snippet with addition domain, added Marketo snippet
* Made fonts consistent, styled note and warning in TS/Akka colors
Merge pull request #16140 from akka/wip-doc-new-style-2.3-ban

(Validation back port) =doc New styling and logos for the documentation