Make property optional only if to-one relationship marked as optional…

… (swift).

templates/machine.swift.motemplate

@@ -83,7 +83,7 @@ class _<$managedObjectClassName$>: <$customSuperentity$> {
 
 <$else$>
     @NSManaged
-    var <$Relationship.name$>: <$Relationship.destinationEntity.managedObjectClassName$>?
+    var <$Relationship.name$>: <$Relationship.destinationEntity.managedObjectClassName$><$if Relationship.isOptional$>?<$endif$>
 
     // func validate<$Relationship.name.initialCapitalString$>(value: AutoreleasingUnsafePointer<AnyObject>, error: NSErrorPointer) {}
 <$endif$>