add global sticky navbar option

[apreshill]

If I set the sticky menu globally, it only affects pages, it still doesn't affect the home page, or any other pages like sitemap or the single card pages in the demo site:

params:
  pageFeatures: [+sticky_menu]

To get the sticky menu to work for those pages, I had to set it individually in the _index.md front matter. I think this is a bit confusing- can you add a global sticky menu option?