WMF: fixed MediaPlayer buffering logic.

To have a consistent behavior with other backends, the WMF plugin now
starts the session after loading a media in order to start buffering some
data and correctly notify when the media is buffered.
It was previously reporting a BufferedMedia status only (and wrongly)
after explicitly starting the media player.

Not all source readers (usually a source reader is specific to a file
format) implement the service needed to query buffering progress. In that
case just report the media to be buffered immediately after loading.

Change-Id: I6e6332ae08e96fc789556761e5169b88c36c5e37
Reviewed-by: Christian Stromme <christian.stromme@digia.com>
DirectShow: Don't create the widget and renderer controls until requested.

Task-number: QTBUG-32282
Change-Id: If37ed4c35bcc2cc879f50d3b2ea3720b90603e9a
Reviewed-by: Yoann Lopes <yoann.lopes@digia.com>
DirectShow: avoid unnecessary RGB32 -> BGR32 conversion.

Frames in the RGB32 format are actually using the BGR byte order, no need
to do the conversion.

Task-number: QTBUG-29206
Change-Id: I13527bd9dacc8330df78beb0965b31469c1d7a87
Reviewed-by: Yoann Lopes <yoann.lopes@digia.com>
Merge remote-tracking branch 'origin/stable' into dev

Change-Id: If52332b72560d21069e24cd31b13f08f33e1f406