Codegen: Create internal folders

misc/codegen/templates/ql_class_public.mustache

@@ -1,9 +1,9 @@
 // generated by {{generator}}, do not edit
 /**
- * This module provides the public class `{{name}}`.
+ * This module provides the {{^internal}}public {{/internal}}class `{{name}}`.
  */
 
-private import {{name}}Impl
+private import {{^internal}}internal.{{/internal}}{{name}}Impl
 {{#imports}}
 import {{.}}
 {{/imports}}