constructor(props) {
        super(props);
        this.stepChildren = [];
        this.numbersMap = {};
        this.registerStep = this.registerStep.bind(this);
        this.setChildrenState = this.setChildrenState.bind(this);
    }
The ProgressIndicator is a visual representation of a user's progress through a set of steps.
To add the steps, you will need to implement the `ProgressStep` component.