CORD-2049: Fill gap in support for attics. Support for attics to
continue, even if deprecated

Change-Id: Icf794ace07b63f76d4bbec1f5180652881dc909a
(cherry picked from commit ba75f4aa88770f611a2dd40e0954b3c3c5ef7cd5)
diff --git a/lib/xos-genx/xosgenx/targets/service.xtarget b/lib/xos-genx/xosgenx/targets/service.xtarget
index 69aa81c..ceb173c 100644
--- a/lib/xos-genx/xosgenx/targets/service.xtarget
+++ b/lib/xos-genx/xosgenx/targets/service.xtarget
@@ -2,10 +2,14 @@
 {% set legacy_tag = '_decl' %}
 {% set legacy = True %}
 from core.models.xosbase import *
+from core.models import ServiceInstance
+from django.db import models
+from django.db.models import *
+from core.models.xosbase import StrippedCharField
 {% else %}
 {% set legacy = False %}
 {% set legacy_tag = '' %}
-from header import *
+{% if file_exists('header.py') -%}from header import *{% endif %}
 {% endif %}
 
 {% for m in proto.messages %}