Listen for recipient changes in conversations and group updates.

Closes #4079
// FREEBIE

src/org/thoughtcrime/securesms/recipients/Recipient.java

@@ -179,7 +179,7 @@ public class Recipient {
     }
 
     for (RecipientModifiedListener listener : localListeners)
-      listener.onModified(Recipient.this);
+      listener.onModified(this);
   }
 
   public interface RecipientModifiedListener {

src/org/thoughtcrime/securesms/recipients/Recipients.java

@@ -185,9 +185,7 @@ public class Recipients implements Iterable<Recipient>, RecipientModifiedListene
       }
     }
 
-    synchronized (this) {
-      listeners.add(listener);
-    }
+    listeners.add(listener);
   }
 
   public synchronized void removeListener(RecipientsModifiedListener listener) {