Add different levels of relevance as a relation between parent topics and topic children

[emwalker]

Let's take a first pass at adding levels of relevance to the relationship between a parent topic and its children. E.g.,

• High
• Medium
• Low
• Questionable
• Review

By default, querying with the "Low" relevance selected will bring up items with medium and high relevance as well and in general will return a lot of items.

There will be a role or permission that enables specific users to move a given link or topic to a higher level of relevance for a specific parent topic. The user will be a moderator or curator for that parent topic. Ideally the user will have some expertise in the parent topic. The role or permission will transitively apply to subtopics (we'll need to figure out how to prevent this from becoming a vector to gain moderation access to another topic, though).

Both topics and links will have a relevance to a given parent topic.

Eventually this feature might be extended to allow for ad hoc "contexts" that will make it possible to retrieve the results found in an earlier research project. Presumably these contexts would be private, but maybe not.