1. SiteInfo should be renamed to AssociatedContent
2. The is_content_association_possible field should be removed - the presence/absence of AssociatedContent should imply whether its possible.
3. The optional fields on AssociatedContent should be made non-optional. They were originally set to optional as the struct was always present. Now it will only be present when there is AssociatedContent.
4. Remove the hostname field - its inferrable from the url field and adds nothing

This cleanup will make adding support for associating multiple bits of content far easier.