shouldComponentUpdate

    shouldComponentUpdate (nextProps) {
        // have any of the items changed?
        if(!isArrayEqual(this.props.items, nextProps.items)){
            return true;
        }
        // everything from here is horrible.

        // if interaction has not changed at all then when can return false (yay!)
        if(isObjectEqual(this.props.interaction, nextProps.interaction)){
            return false;
        }

        // at this point we know:
        //      1. the items have not changed
        //      2. the interaction has changed
        // we need to find out if the interaction change was relevant for us

        const wasItemSelected = this.props.items.any(item => {
            return item.id === this.props.interaction.selectedId
        });
        const isItemSelected = nextProps.items.any(item => {
            return item.id === nextProps.interaction.selectedId
        });

        // return true when something has changed
        // return false when nothing has changed
        return wasItemSelected !== isItemSelected;
    }