Todo: Better naming of enum value.

It's not the last, it's the count.

Change-Id: Ib739c34b952af022f83fa0c2d547154d70641456
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@digia.com>

src/plugins/todo/todoitemsmodel.cpp

@@ -70,7 +70,7 @@ int TodoItemsModel::columnCount(const QModelIndex &parent) const
 {
     Q_UNUSED(parent)
 
-    return Constants::OUTPUT_COLUMN_LAST;
+    return Constants::OUTPUT_COLUMN_COUNT;
 }
 
 QVariant TodoItemsModel::data(const QModelIndex &index, int role) const