UI: Update header
Please implement the new header layout:
Design in https://www.figma.com/file/oXHipxIouyWvGgERlMtcyZ/01-Gynesis_BlogPage?node-id=0%3A481
Notes:
- Mobile header has one hamburger in the right corner. We'll include the login options in it.
- Otherwise, the header seems to be centered (like the content)
- It seems that links to "content" are blue
- Menus open on click (and not hover)
- Login menu should open the popup below, and if logged-in, then we will use the blue links.