Correctly identify supported formats in QMediaImageViewer.
Correctly identify supported formats in QMediaImageViewer.

Get a list of supported extensions from QImageReader rather than
relying on a potentially inaccurate static list of formats.

Task-number: MOBILITY-1756
Reviewed-by: Justin McPherson

enthought/qt-mobility,qtproject/qt-mobility,kaltsi/qt-mobility,kaltsi/qt-mobility,qtproject/qt-mobility,tmcguire/qt-mobility,enthought/qt-mobility,tmcguire/qt-mobility,kaltsi/qt-mobility,enthought/qt-mobility,KDE/android-qt-mobility,qtproject/qt-mobility,KDE/android-qt-mobility,enthought/qt-mobility,qtproject/qt-mobility,KDE/android-qt-mobility,enthought/qt-mobility,kaltsi/qt-mobility,tmcguire/qt-mobility,qtproject/qt-mobility,tmcguire/qt-mobility,KDE/android-qt-mobility,tmcguire/qt-mobility,qtproject/qt-mobility,kaltsi/qt-mobility,enthought/qt-mobility,kaltsi/qt-mobility