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/DlgSettingsColorGradientImp.cpp

@@ -84,7 +84,7 @@ DlgSettingsColorGradientImp::~DlgSettingsColorGradientImp()
 
 void DlgSettingsColorGradientImp::setupConnections()
 {
-    QButtonGroup* group = new QButtonGroup(this);
+    auto group = new QButtonGroup(this);
     group->setExclusive(true);
     group->addButton(ui->radioButtonFlow);
     group->addButton(ui->radioButtonZero);