medication identifier

<MedicationDispense>
   ...
   <medicationReference>
	<reference value="urn:uuid:9c7e61c3-5b92-4828-9ebc-21e74bcdbc96"/>
   </medicationReference>
   ....
</MedicationDispense>

or 

<MedicationDispense>
   ...
   <medicationReference>
	<reference value="https://fhir.someterminologyserver.nhs.uk/Medication/31771611000001107"/>
   </medicationReference>
   ....
</MedicationDispense>


Becomes 

<MedicationDispense>
   ...
   <medicationReference>
	  <display value="BD Viva hypodermic insulin needles for pre-filled / reusable pen injectors screw on 5mm/31gauge (Becton, Dickinson UK Ltd)"/>
          <identifier>
                <system value="http://snomed.info/sct"/>
                <value value="31771611000001107"/>
          <identifier>
   </medicationReference>
   ....
</MedicationDispense>

or (using ITK profile, reference is mandatory)

<MedicationDispense>
   ...
   <medicationReference>
          <reference value="https://fhir.someterminologyserver.nhs.uk/Medication/31771611000001107"/>
	  <display value="BD Viva hypodermic insulin needles for pre-filled / reusable pen injectors screw on 5mm/31gauge (Becton, Dickinson UK Ltd)"/>
          <identifier>
                <system value="http://snomed.info/sct"/>
                <value value="31771611000001107"/>
          <identifier>
   </medicationReference>
   ....
</MedicationDispense>