Add Key Visual into website header (homepage)

[wittwitsan]

After waiting for so long, it's time to iterate the website header with the Key Visual.

Background assets here: https://drive.google.com/open?id=1DNwXZg-th9WsdEon7DHq06EEDUMEA1X4

• [ ] WordCamp Asia 2020 -> Rubik / Bold / font-size 30.17px / line-height 36px / #D73534
• [ ] February 21-23, Bangkok, Thailand -> Roboto Slab / Regular / font-size 16.97px / line-height 22px / #36393B
• [ ] Space between logo and "WordCamp Asia 2020" -> 19px
• [ ] Space between "WordCamp Asia 2020" and "February 21-23, Bangkok, Thailand" -> 4px

[tepkenvannkorn]

@drebbits should we keep "21st Contributor Day / 22nd & 23rd Conference Day"?

[drebbits]

@tepkenvannkorn let's keep it for now. Thanks for the updates here!