Wrap layer images with a div. One div per layer

wrap-layer-images.js

wp.hooks.addAction( 'PC.fe.viewer.item.added', 'MKL/PC/Custom_JS', function( view, viewer ) {
    // Set the class name
    var layer_class = 'layer-' + view.model.get( 'layerId' );
    // Find the existing container.
    var layer_container = viewer.$layers.find( '.' + layer_class );
    if ( ! layer_container.length ) {
        // If the container doesn't exist, add it
        view.$el.wrap( '<div class="' + layer_class + '" />' );
	} else {
        layer_container.append( view.$el );
	}
} );