Gui: Use auto and range-based for (#7481)

* On lines where the variable type is obvious from inspection, avoid repeating the type using auto. 
* When possible use a ranged for loop instead of begin() and end() iterators

src/Gui/TreeView.cpp

@@ -79,7 +79,7 @@ void TreeView::rowsInserted (const QModelIndex & parent, int start, int end)
 {
     QTreeView::rowsInserted(parent, start, end);
     if (parent.isValid()) {
-        Base::BaseClass* ptr = static_cast<Base::BaseClass*>(parent.internalPointer());
+        auto ptr = static_cast<Base::BaseClass*>(parent.internalPointer());
         // type is defined in DocumentModel.cpp
         if (ptr->getTypeId() == Base::Type::fromName("Gui::ApplicationIndex")) {
             for (int i=start; i<=end;i++) {