loadSubmission() {
        this.loadingSubmission = true;
        if (this.formio.submissionId) {
            this.onSubmission = this.formio
                .loadSubmission()
                .then(
                    (submission) => this.setSubmission(submission),
                    (err) => this.submissionReadyReject(err)
                )
                .catch((err) => this.submissionReadyReject(err));
        } else {
            this.submissionReadyResolve();
        }
        return this.submissionReady;
    }
Loads the submission if applicable.
@returns {Promise} - The promise that is triggered when the submission is loaded.