restructure generator

templates/model_prelude.hbs

@@ -0,0 +1,9 @@
+use {{prelude_path}}::*;
+use sea_orm::ActiveModelBehavior;
+
+#[async_trait::async_trait]
+impl ActiveModelBehavior for {{active_model_name}} {}
+
+impl {{model_name}} {}
+
+impl {{active_model_name}} {}