direct2d: inherit VideoRenderer to avoid QImage construct

TODO:
1. need a function call when setSourceSize() called
2. try QPainter::beginNativePaint()
3. try to implement other QPaintEngine. What Qt has?
direct2d: check ptr

BUG:
sometimes windows give this error: "D3D11: Removing Device"
even the user will logout the system!
direct2d: showEvent instead of changeEvent to avoid flicker when active
state changed