MS a link between two claims can have a pro/con polarity attached

[Venryx]

User-interface:

• When right-clicking a node, the "Add structured child (re. )" item should have two children (when valid for the right-clicked node): "New supporting claim", "New opposing claim"
• These buttons should open the dialog to add a new claim (similar to the "Add freeform child -> New claim" option), except rather instead of adding a node-link entry of {type: "freeform}, it should add one of {type: "truth"/"relevance"} (depending on child-group being added to), and with the polarity field (in the link) set to supporting or opposing.
• The node-ui components may also need some updating to support the case of a child of type claim having a pro/con polarity. (historically, the only times where pro/con "polarity" were assigned is for children nodes of the argument type, not claim, so some sections of the frontend code may get confused or error due to the new case being introduced)