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/git/branchadddialog.cpp

@@ -125,7 +125,7 @@ BranchAddDialog::BranchAddDialog(const QStringList &localBranches, Type type, QW
         break;
     }
 
-    using namespace Utils::Layouting;
+    using namespace Layouting;
 
     Column {
         Row { branchNameLabel, m_branchNameEdit },

src/plugins/git/branchcheckoutdialog.cpp

@@ -45,7 +45,7 @@ BranchCheckoutDialog::BranchCheckoutDialog(QWidget *parent,
 
     auto buttonBox = new QDialogButtonBox(QDialogButtonBox::Cancel|QDialogButtonBox::Ok);
 
-    using namespace Utils::Layouting;
+    using namespace Layouting;
 
     Column {
         m_makeStashRadioButton,

src/plugins/git/gerrit/gerritpushdialog.cpp

@@ -136,7 +136,7 @@ GerritPushDialog::GerritPushDialog(const Utils::FilePath &workingDir, const QStr
     connect(m_buttonBox, &QDialogButtonBox::accepted, this, &QDialog::accept);
     connect(m_buttonBox, &QDialogButtonBox::rejected, this, &QDialog::reject);
 
-    using namespace Utils::Layouting;
+    using namespace Layouting;
 
     Grid {
         ::Git::Tr::tr("Push:"), workingDir.toUserOutput(), m_localBranchComboBox, br,