Assessment list view rework

Summary

This merge request:

• replaces the assessment list view with a React-based view
• adds a filtering/search option to that view
• adds an 'organisation list' view which lists organisations now it's not on the assessment list
• switches all the views that aren't the assessment editor to use the same HTML/JS bundle and both server & client side routing
• drops /v2/ from all URLs with appropriate redirects

Checklist

• Documentation impact considered
• Manual smoke test run (if possible)
• Local-only tests run
• Assigned related ticket to reviewer

Related to #464