Update the Categorization module for 5.4 and catfn.

Planning:

• What is a category? How to use them on your site? Explain why tour types and destinations are categories in the travel demo.
• Using the Categories app vs. creating a dedicated app such as Tour Categories. Pros and cons.
• Tagging content. Adding a category link or category tab to a form.
• catfn use cases:
  • Finding content for a category
  • Showing the categories of content