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:

1. Mobile header has one hamburger in the right corner. We'll include the login options in it.
2. Otherwise, the header seems to be centered (like the content)
3. It seems that links to "content" are blue
4. Menus open on click (and not hover)
5. Login menu should open the popup below, and if logged-in, then we will use the blue links.