* common Picture : Introduce Picture's size setter, getter APIs
If picture or file loaded by picture has an explicit Size(width, height),
it is transformed to fit the size.
in the last commit, it added a raw image file in the images folder.
It breaks Multicanvas, Svg which try to load all kinds of files in it.
We don't need to load all files by figuring out file extension name.
Move the Clear call to the end of drawing those scenarios doesn't need to retain paints resources.
We should show the examples as the best usage.
@Issues: 75
