add filter to allow customizing where the dropdown filter is shown

Author: k1sul1

classes/class-cpt-wplf-submission.php

@@ -107,6 +107,7 @@ function form_filter_dropdown() {
     global $pagenow;
 
     $allowed = array("wplf-submission"); // show filter on these post types (currently only one?)
+    $allowed = apply_filters("wplf-dropdown-filter", $allowed);
     $post_type = get_query_var("post_type");
 
     if( 'edit.php' != $pagenow || !in_array($post_type, $allowed)) {