Redefine "model" as an attribute

Author: rayosborn

base_classes/NXparameters.nxdl.xml

@@ -41,7 +41,7 @@
         have been defined to store metadata associated with such a
         refinement.       
     </doc>
-    <field name="model">
+    <attribute name="model">
         <doc>
             The name of the model used in optimizing the parameter
             values. Fitting packages such as LMFIT
@@ -50,7 +50,7 @@
             attribute is provided, it is assumed that all the parameters
             in this group are associated with this model.
         </doc>
-    </field>
+    </attribute>
     <field name="PARAMETER" type="NX_CHAR_OR_NUMBER" nameType="any">
         <doc>
             A parameter that is used in or results from processing.