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/bazaar/bazaarplugin.cpp

@@ -286,7 +286,7 @@ public:
         dryRunBtn->setToolTip(Tr::tr("Test the outcome of removing the last committed revision, without actually removing anything."));
         buttonBox->addButton(dryRunBtn, QDialogButtonBox::ApplyRole);
 
-        using namespace Utils::Layouting;
+        using namespace Layouting;
         Column {
             Form {
                 keepTagsCheckBox, br,