Gui: fix Std_Transform tool

The problem is caused by tracking of editing object placement
introduced in 719c11e.

After this commit, any editing object can disable placement tracking by
calling Gui::Document::setEditingTransform() inside either
ViewProvider::startEditing() or setEditingViewProvider().

src/Gui/Document.cpp

@@ -404,19 +404,21 @@ bool Document::setEdit(Gui::ViewProvider* p, int ModNum, const char *subname)
             d->_editSubname = subname;
     }
 
+    auto sobjs = obj->getSubObjectList(subname);
+    d->_editObjs.clear();
+    d->_editObjs.insert(sobjs.begin(),sobjs.end());
+    d->_editingObject = sobj;
+
     d->_editMode = ModNum;
     d->_editViewProvider = svp->startEditing(ModNum);
     if(!d->_editViewProvider) {
         d->_editViewProviderParent = 0;
+        d->_editObjs.clear();
+        d->_editingObject = 0;
         FC_LOG("object '" << sobj->getFullName() << "' refuse to edit");
         return false;
     }
 
-    auto sobjs = obj->getSubObjectList(subname);
-    d->_editObjs.clear();
-    d->_editObjs.insert(sobjs.begin(),sobjs.end());
-    d->_editingObject = sobj;
-
     if(view3d) {
         view3d->getViewer()->setEditingViewProvider(d->_editViewProvider,ModNum);
         d->_editingViewer = view3d->getViewer();

src/Gui/ViewProviderDragger.cpp

@@ -214,6 +214,7 @@ void ViewProviderDragger::setEditViewer(Gui::View3DInventorViewer* viewer, int M
       csysDragger->setUpAutoScale(viewer->getSoRenderManager()->getCamera());
 
       auto mat = viewer->getDocument()->getEditingTransform();
+      viewer->getDocument()->setEditingTransform(mat);
       auto feat = dynamic_cast<App::GeoFeature *>(getObject());
       if(feat) {
           auto matInverse = feat->Placement.getValue().toMatrix();

src/Gui/ViewProviderLink.cpp

@@ -2408,6 +2408,7 @@ bool ViewProviderLink::initDraggingPlacement() {
     dragCtx.reset(new DraggerContext);
 
     dragCtx->preTransform = doc->getEditingTransform();
+    doc->setEditingTransform(dragCtx->preTransform);
 
     const auto &pla = ext->getPlacementProperty()?
         ext->getPlacementValue():ext->getLinkPlacementValue();