adding animation to extra-info title, and mild restructure

Added the animation as discussed here 

https://meta.discourse.org/t/should-category-go-below-the-topic-title-on-the-topic-page/20377/78

Edited header.hbs so:
* the star doesn't show alongside the "loading topic" or "topic error" message
* I can target error/loading messages in extra-info (so I can prevent those from animating; looks wonky if they do)

:telescope: :crocodile: