Tagging and linking

[Ninjani]

Think about more tagging and linking functionality. Some ideas:

• [ ] Linking an annotation to another like a footnote. Maybe with a special tag like gooseberry_link_a1_a2, or using the references field in Annotation.
• [x] Tags can probably be parents of other tags: e.g Science -> Biology. In mermaid this would be a subgraph but how would this be indicated by the user? gooseberry_parent_t1_t2?
• [ ] Need to deal with reply comments correctly and nest them in the wiki. This could also be a CLI functionality gooseberry reply to mark one annotation as the child of another. This also uses the references field in Annotation.