Change (fix) preview display ratio between 4:3 and 16:9

In Symbian the viewfinder ratio is directly coupled with the current image capture dimension. Thus, at the moment it is only possible to change the ratio with Qt Mobility by capturing a picture in the respective ratio.
This should be fixed so that the ratio can be changed without capturing a picture. Therefore the Symbian method "CCamera::PrepareImageCaptureL(CCamera::EFormatExif,DIMENSION_INDEX)" has to be called before the camera is started.