implemented transfer of list ownership. this resolves #4

Signed-off-by: Stephan Richter <s.richter@srsoftware.de>

src/main/java/de/srsoftware/widerhall/data/User.java

@@ -326,4 +326,9 @@ public class User {
     public String token() {
         return token;
     }
+
+    @Override
+    public String toString() {
+        return name == null ? email : name;
+    }
 }