CanDelete is necessary for dimensions

- therefore revert commit bd0bf690b53f8355400278a127524029d225dffb.
- handle balloons the same way
- fix line ending in ViewProviderProjGroupItem.cpp

src/Mod/TechDraw/Gui/ViewProviderBalloon.cpp

@@ -180,3 +180,11 @@ void ViewProviderBalloon::handleChangedPropertyType(Base::XMLReader &reader, con
         LineWidth.setValue(LineWidthProperty.getValue());
     }
 }
+
+bool ViewProviderBalloon::canDelete(App::DocumentObject *obj) const
+{
+    // deletions of a balloon object doesn't destroy anything
+    // thus we can pass this action
+    Q_UNUSED(obj)
+    return true;
+}