Utils: Make Layouting a top level namespace

The whole machinery is now almost only layoutbuilder.{h,cpp},
mostly independent of the rest of Utils. Idea is to finish the
separation to make it stand-alone usable also outside creator.

Change-Id: I958aa667d17ae26b21209f22412309c5307a579c
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

src/plugins/copilot/authwidget.cpp

@@ -22,7 +22,7 @@ namespace Copilot {
 AuthWidget::AuthWidget(QWidget *parent)
     : QWidget(parent)
 {
-    using namespace Utils::Layouting;
+    using namespace Layouting;
 
     m_button = new QPushButton(Tr::tr("Sign in"));
     m_button->setEnabled(false);