ONS: Download categories tree and CSV files

• As a system
• I want to obtain categories and CSV files from ONS website
• In order to store the hierarchy of information for ONS

Acceptance criteria

• All categories branches MUST end with a CSV file
• Each dataset page MUST be stored as an HTML file in order to keep its description paragraph that follows the title
• Categories pages SHOULD be stored as HTML files in sub-directories reproducing the URL paths
  • OR produce a JSON of categories hierarchy if simpler

Technical tasks

• Start with page https://www.ons.gov.uk/
• Parse HTML pages related to menu entries: Business, Industry and Trade; Economy; Employment and Labour Market; People, population and community (class="primary-nav__list")
• Open link with green background named "View all datasets related to FOO"
• Items with string "Dataset ID: XXXX" have a corresponding CSV file (to be verified with an assertion). Ignore others.
• Parse each HTML pages until finding CSV files (CSV files following <h2>Your download options</h2>)
• A branch that doesn't have a CSV file as a leave MUST be pruned