UI changes

Changes to the UI based on user research feedback.

Of the interesting changes:
  * Use tabs instead of buttons, to navigate different need functionality
  * 'Mark as out of scope' and 'Close as a duplicate' now appear in a new Actions tab
  * 'Close as duplicate' now has a modal version when JS is running, like 'Mark as out of scope'
  * 'Save and add a new need' to reduce user clicks when entering multiple needs.
  * Workflow buttons now appear on a fixed bottom navigation bar.

Other changes relate to CSS changes/additions, splitting up test files, and fixing tests based on the new UI.