Add featured post by same tags

[ajfisher]

To determine the featured post that should appear on the page. Do the following:

• If not a post then take the most recent
• Check the current post for tags then iterate over the featured post list and find the post with the highest overlap of tags. Display that one.
• If a tag page, check for featured post that matches this tag, if can't find then use most recent. If can find then use the same as the header one.

[ajfisher]

Don't need to do this so much as simply make another graphql query for the featured post that matches the tag.

If featured comes back null then the featured post becomes the top ranked item from the main post list.