Don't append dates or separator if they are already in the discussion

Fix #483

app/widgets/Chat/chat.js

@@ -527,9 +527,13 @@ var Chat = {
     },
     appendDate: function(date, prepend) {
         var list = document.querySelector('#chat_widget > div ul');
+
+        if(document.getElementById(MovimUtils.cleanupId(date))) return;
+
         dateNode = Chat.date.cloneNode(true);
         dateNode.dataset.value = date;
         dateNode.querySelector('p').innerHTML = date;
+        dateNode.id = MovimUtils.cleanupId(date);
 
         var dates = list.querySelectorAll('li.date');
 
@@ -554,6 +558,9 @@ var Chat = {
         separatorNode = Chat.separator.cloneNode(true);
 
         var list = document.querySelector('#chat_widget > div ul');
+
+        if(list.querySelector('li.separator')) return;
+
         var messages = document.querySelectorAll('#chat_widget > div ul div.bubble p');
 
         if(messages.length > counter && counter > 0) {