Quick fix: image size property update

This is a bit of a workaround for scalable image nodes to update the
current size rather than only the original one. This is done so the
MediaSizeWidget in the media edit dialog is fed the current dimensions
of the image even without the image being saved.

Ideally, the node's 'currentDimensions' property should be constantly
updated to current dimensions. This workaround fixes the given bug, in
which all images show the original wikitext/default size even after
being resized.

Bug: 61052
Change-Id: I902d1f51b1389f2f9b2b5c871b578ee2244a946f
Merge "Quick fix: image size property update"