Use SVM (metafile) instead of PNG for diagrams (SmartArt)

It seemed a bit pointless to waste CPU cycles on PNG-compressing a
bitmap image only to later then uncompress it anyway. vcl's PNG
writing code showed up as 13% on the time profile of TiledLibreOffice
when displaying a document full of SmartArts.

Miklos suggested I try using SVM (which I guess means "StarView
Metafile") instead. When using SVM, no rendering of diagrams to
bitmaps during loading is done, but the diagram stays stored in a
resolution-independent (vector-ish) form. Which means it will be
rendered nicely and crisply regardless of the zoom level.

At least, that is my understanding, and experimentation (on OS X and Linux)
seems to confirm.

ce8c0ff07559ddcc729bffd7a68f4c6f281882e3

Change-Id: Ice8c0ff07559ddcc729bffd7a68f4c6f281882e3