PinWidget (see "BTW" at https://bugs.kde.org/show_bug.cgi?id=335399#c1)

umbrello/widgets/portwidget.{h,cpp}
- New function ownerWidget() encapsulates extraction of owning
  ComponentWidget.
  Motivation: Implementation will be different for PinWidget.
- Rename function attachToOwningComponent() to attachToOwner().
  Motivation: Prepare for applicability to PinWidget (owner of PinWidget is
  not a ComponentWidget).
- Rename function slotCompMoved() to slotOwnerMoved().
  Motivation: Prepare for applicability to PinWidget.
- In C++ body, replace mentions of m_umlObject->name() by name().
  Motivation: Prepare for common base class (m_umlObject of PinWidget is
  always NULL).

umbrello/umlscene.cpp
- Adapt function setupNewWidget() to renamed PortWidget function
  attachToOwner().