Switch out existing obfuscated license with external module

This creates a new fallback license module called StubLicense that
will be used in the event that the tower_license module is not
installed.

All existing license mechanisms are routed through the get_licenser()
util method

awx/api/views.py

@@ -324,9 +324,9 @@ class ApiV1ConfigView(APIView):
                         extra=dict(actor=request.user.username))
             return Response({"error": _("Invalid JSON")}, status=status.HTTP_400_BAD_REQUEST)
         try:
-            from awx.main.task_engine import TaskEnhancer
+            from awx.main.utils.common import get_licenser
             license_data = json.loads(data_actual)
-            license_data_validated = TaskEnhancer(**license_data).validate_enhancements()
+            license_data_validated = get_licenser(**license_data).validate()
         except Exception:
             logger.warning(smart_text(u"Invalid license submitted."),
                            extra=dict(actor=request.user.username))