add tone attribute to memory

src/main/java/de/fuberlin/imp/memorybox/restmembox/model/Memory.java

@@ -26,7 +26,7 @@ public class Memory {
 
     private byte[] voice;
     private String voiceText;
-    // enum tone
+    private Tone tone;
     private byte[] image;
     private String note; // optional Text
     private Weather weather;