Fix the spinner not spinning on the main site

fixes #3394
Use the same spinner styles as Marketplace.

* Reduces the "wobble"
* Inlines the image for performance

fixes #3404
fixes #3349
The spinner is now inlined in the CSS. Remove it here.
Merge pull request #3395 from mozilla/issue_3394_main_site_spinner

Fix the spinner (main site and it's wonkiness)