Spreadsheet: [skip ci] Fix several clazy issues:

* Mixing iterators with const_iterators [-Wclazy-strict-iterators]
* Q_PROPERTY should have either NOTIFY or CONSTANT [-Wclazy-qproperty-without-notify]
* Missing reference in range-for with non trivial type [-Wclazy-range-loop-reference]
* Missing emit keyword on signal call SpreadsheetGui::SheetViewHeader::resizeFinished [-Wclazy-incorrect-emit]
* Missing emit keyword on signal call QAbstractItemModel::dataChanged [-Wclazy-incorrect-emit]
* c++11 range-loop might detach Qt container (QStringList) [-Wclazy-range-loop-detach]

src/Mod/Spreadsheet/Gui/SpreadsheetView.cpp

@@ -581,7 +581,7 @@ Py::Object SheetViewPy::getattr(const char * attr)
     if (name == "__dict__" || name == "__class__") {
         Py::Dict dict_self(BaseType::getattr("__dict__"));
         Py::Dict dict_base(base.getattr("__dict__"));
-        for (auto it : dict_base) {
+        for (const auto& it : dict_base) {
             dict_self.setItem(it.first, it.second);
         }
         return dict_self;