Liked/likes collections

[srosset81]

https://www.w3.org/TR/activitypub/#liked
https://www.w3.org/TR/activitypub/#likes

• Attach liked AS collections to the WebID
• Attach likes AS collections to resources (for ActivityPods, we create them only when related activities are sent)
• Handle side effects
  • When receiving or emitting Like activities, add the corresponding items to the liked/likes AS collections.