Conditionally call PersistRelations()

Currently, every time `UpdateTopic` is called, `@DeleteRelationships` is called, and then all relationships are resaved via `PersisRelations()`. This adds unnecessary overhead when references aren't all resolved, as we know we're going to have to call `Save()` on those topics _again_ once the topic graph has been saved.

To reduce this overhead, we're now conditionally calling `PersistRelations()` based on the `areReferencesResolved` flag.

_Note:_ The `@DeleteRelationships` parameter is also conditionally set based on this—but that was inadvertantly committed as part of a previous commit (0c860ae). Whoops! Future readers: I apologize or the messy commit history.

Author: JeremyCaney

OnTopic.Data.Sql/SqlTopicRepository.cs

@@ -466,7 +466,9 @@ void addUnmatchedAttribute(string key) {
           "The call to the CreateTopic stored procedure did not return the expected 'Id' parameter."
         );
 
-        PersistRelations(topic, connection, true);
+        if (areReferencesResolved) {
+          PersistRelations(topic, connection, true);
+        }
 
         topic.VersionHistory.Insert(0, version.Value);