Avoid a potential image loss in SwGrfNode::SwapOut() method.

It's better to be explicit when to swap out as a link.
Before if an embedded image swap out failed (e.g. i/o error)
than swap out it as a link could lead to image loss.

Change-Id: I70dd00d5f82c5f4f622805e1d6ee1dfc30900b31
Remove unused Graphic member of SwOLENode

Change-Id: Iaff7e86a8e11e9befc6feacdafd3a78a1971bbcd
Swaping Graphic is a privilage of GraphicObject.

This means more things:
* Graphic won't swap out itself, so those classes which uses
Graphic without GraphicObject won't need to deal with swapping.
* When a Graphic is queried from GraphicObject the caller won't
need to deal with swapping, because GraphicObject swaps it in
before return.
* GraphicObject will swap in the Graphic always when a swapping
dependent data is queried (e.g. whole graphic, transformed graphic
or AnimationNotifyHdl)

Change-Id: I2bf6e37291ec94146f10aac4a35084682437ed16
Why to have this compromise, do that what we say the users we do.

Change-Id: Ia599644ff1f7591ac84bdca988883eaf5860297e