video: use QVideoSink/VideoOutput and QVideoFrame instead of QImage

Removes the rendermanager and framewrapper objects along with any
QQuickPaintedItem-based QML render widget classes. This simplifies
the video widget stack implementation.

The new mechanism uses the VideoOutput component of QtMultimedia.
By accessing the VideoOutput's QVideoSink object, we update the
mapped buffer data of a sink's QVideoFrame when new frames are
published. Updates to frames and component sink subscriptions are
managed by a new class called VideoProvider.

Gitlab: #500
Also #536

Change-Id: I2391a32294922ea435ab80ac1f876c004ff6c21e