Each scene could conserve its own transformation,
the origin could be the parent Paint (if they were beloned to)
Thus, you can compose the multi-tranformed scene group which
simultenoulsly working in own spaces.
See testTransform and testSceneTransform, how they work.
Change-Id: I51deb4d66f8fcd024f8dc7a1e1af57c398a9d7fe
Scene is a group(list) of paints.
This class is designed for vector data set which is prepared before canvas.
If a set of vector data is loaded from other resources such as files,
they can construct these data set using Scene.
This then can be pushed into canvas as one completed image.
Scene is supposed to be used in svg loading and storing to tvg specific data format(tvg)
Change-Id: Ie2ffebf74e79c59d99a77880630a54b6baad7eec
