Hero header

Building #6

* [x] Build `js` component structure
* [x] Add gif animated background by default (center in visible area)
* [ ] ~~Load youtube video (using the video api) as background on larger devices~~ new PR
* [x] add centered text with gain12's characteristics, and loop all off them (center in visible area)
* [x] Scroll down for more information when at scroll top, fade out when scrolling down
Hmm perfect line comment, at the correct line, thanks @T-888!