Draft: [graph/win32] Implement smooth resizing.

The window creation and the message loop has to be put in a separate thread in order to achieve smooth resizing. Othrewise, the modal loop cannot be interrupted to update the canvas. The main thread also has a loop to receive the reposted messages, to update the canvas and send WM_PAINT back (UpdateWindow). After this update the win32 resizing feels similar to the X11 resizing.