default void addChild(RedUINode child) {
        getOurChildren().add(child);
        child.setParent(this);
        final RedUIRootNode root = getRoot();
        child.getSubTree(n -> true).forEach(n -> n.setRoot(root));
        child.onAddedToParent();
    }
Adds a child node to this node. This will set the given node's parent to this node,
and set the root of all nodes in its subtree to this node's root. After,
{@link RedUINode#onAddedToParent()} is called on the newly added child.

@param child The child to add
core/src/main/java/mrtjp/projectred/redui/RedUINode.java