Show cached conversations list before getting list from the server

lib/helpers/conversations_helper.dart

@@ -43,6 +43,13 @@ class ConversationsHelper {
     }
   }
 
+  /// Get the local list of conversations
+  Future<ConversationsList> getCachedList() async {
+    final list = await _conversationsDatabaseHelper.getAll();
+    list.sort();
+    return list;
+  }
+
   /// Get the name of a [conversation]. This requires information about the
   /// users of this conversation
   static String getConversationName(