Implement the new signup screen

This MR should go into a epic/onboarding

New mocks https://projects.invisionapp.com/share/KWU1X9IEB2U#/screens/399136677

• Validates username, email and password
• Enforces password length requirements
• Login link goes to the new login page
• terms of use goes to the terms of use page
• Enforces the "I have read checkbox...."
• e2e tests
• unit tests