Adding properties to HapiProperties:

* subscription.resthook.enabled
* subscription.email.enabled
* allow_placeholder_references

src/main/resources/hapi.properties

@@ -6,6 +6,7 @@ default_page_size=20
 max_page_size=200
 allow_multiple_delete=true
 allow_external_references=true
+allow_placeholder_references=true
 expunge_enabled=true
 persistence_unit_name=HAPI_PU
 logger.name=fhirtest.access
@@ -20,6 +21,8 @@ server.base=/baseDstu3
 server.name=Local Tester
 server.id=home
 test.port=
+subscription.email.enabled=true
+subscription.resthook.enabled=true
 hibernate.dialect=ca.uhn.fhir.jpa.util.DerbyTenSevenHapiFhirDialect
 hibernate.search.model_mapping=ca.uhn.fhir.jpa.search.LuceneSearchMappingFactory
 hibernate.format_sql=false