am#54 - New nav bar menu

Changes

• Introduced developing component JS with typescript, compiling into JS
  • For now am committing up JS artefacts, consistent with the CSS.
• Moved caret to be a twig file
  • Exact same output, but simplifies importing for consistency and simplifies rendering in storybook (without this we need to pass through more Drupal behind-the-scenes props)
• Updated link styles, and added contrast link styles
  • Note these will need moving as part of https://uniofcam.atlassian.net/browse/AM-213
• Added new menu
  • No longer uses jQuery
  • Improved accessibility
  • Improved no-JS fallback
  • New styles to match design
  • Improved keyboard navigation

Out of scope

• The open menu bar styles, HTML and functionality inside that window
• Handling of mobile states
• Handling of too many menu bar items