Video last touches

This pull request fixes up a few small video things:

- The 'more [section] videos' link is now a tag combiner link
- The popular videos component is not shown on the childrens book site, `childrens-books-site`
- The 'more [section] videos' component is filtered of content that matches the series of the current video.
Is it safe to use sectionName here, rather than an id?