Comment 11 for bug 170533

Partially improved patch - but this patch is not ready for committing.
* Performance should be significantly (at least 5x) better
* Crashes (comment #4 and #5) should be fixed
* Missing thumbnails (comment #9) should be fixed
* Preference->Interface->Thumbnail Size : 16/32/48px size thumbnails.

This patch renders the actual on-canvas DrawingItem onto a DrawingContext
Unfortunately it appears there are some issues, possibly due to caching ...
* Items sometimes don't draw into thumbnail after moving, changing
* On-canvas artifacts appear after moving objects

Hopefully an expert like Krzysztof can help with this issue .... any ideas more that welcome.