Show the landing page.

def index():
    """Show the landing page."""
    gene_lists = app.db.gene_lists() if app.config['STORE_ENABLED'] else []
    queries = app.db.gemini_queries() if app.config['STORE_ENABLED'] else []

    case_groups = {}
    for case in app.db.cases():
        key = (case.variant_source, case.variant_type, case.variant_mode)
        if key not in case_groups:
            case_groups[key] = []
        case_groups[key].append(case)

    return render_template('index.html', case_groups=case_groups,
                           gene_lists=gene_lists, queries=queries)