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/fossil/fossilplugin.cpp

@@ -1094,7 +1094,7 @@ RevertDialog::RevertDialog(const QString &title, QWidget *parent)
     connect(buttonBox, &QDialogButtonBox::accepted, this, &QDialog::accept);
     connect(buttonBox, &QDialogButtonBox::rejected, this, &QDialog::reject);
 
-    using namespace Utils::Layouting;
+    using namespace Layouting;
     Form {
         Tr::tr("Revision"), m_revisionLineEdit, br,
     }.attachTo(groupBox);