Fix up a few doc issues

* lingering references to Mobility
* missing group tags on some classes meant they went missing
* put classes into functional groups as well (e.g. audio, camera)
* added some of the qdoc files to OTHER_FILES so they show up in Creator

There are still a lot of warnings since it seems like qdoc is not
processing the controls directory.

Change-Id: I036f8826ae63f8273b3e649cb32c091d964ce830
Reviewed-by: Jonas Rabbe <jonas.rabbe@nokia.com>

src/multimedia/playback/qmediaplaylistprovider.cpp

@@ -52,6 +52,9 @@ QT_BEGIN_NAMESPACE
     \brief The QMediaPlaylistProvider class provides an abstract list of media.
     \inmodule QtMultimedia
 
+    \ingroup multimedia
+    \ingroup multimedia_playback
+
     \sa QMediaPlaylist
 */