Reskin the existing notification drop down into the new designs

Notification dropdown mockup https://projects.invisionapp.com/d/main#/console/18532170/400020222/preview

• Update and move the notification icon to the right hand side.
• Reskin the dropdown
• Shrink the height and display fewer notifications by default
• Change the "View all" text to "See all notifications
• Responsive
• Light mode
• Dark mode
• Unit tests
• e2e tests

changed due date to January 28, 2020

changed milestone to %Sprint::01/15 - Youthful Yabby

added scoped labels

changed weight to 4

added to epic &93