Implement the new login screen

New mocks: https://projects.invisionapp.com/share/KWU1X9IEB2U#/screens/399136674

This MR should go into a epic/onboarding

Since we don't have a mock for login, implement the same design as the signup screen

• new design for login
• new blue hyperlink for "create a channel" and "forgot password"
• language selector on the bottom
• login button should login

I am going to get ping @michaelfbradley about error messages in the mobile designs