Port image editor ImageRegionWidget to Qt4 model/view
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ImageRegionWidget is a Qt3Support class based on Q3ScrollView class (PreviewWidget) which will disapear with next Qt5.
This class is used by digiKam Image editor to render canvas of tools as ColorCorrection, CurvesAdjust, LevelAdjust, etc.
It must be ported to Qt4 model/view implementation using already existing common classes used in digiKam core.

Common classes used to define Model/View digiKam canvas are listed below :

GraphicsDImgView : this class is derived from model/view core implementation based on QGraphicsView to display a zoomable view.

ImagePreviewItem : it's a derivated class from GraphicsDImgItem, which define canvas painting re-implementation

To port ImageRegionWidget to model-view, a new class must be derivated from GraphicsDImgView and a canvas painting implementation must be hosted to
a new dedicated class based on ImagePreviewItem. A similar port has been done with image editor RawPreview class which is the preview 
implmentation of editor RAW file import tool.

Port image editor Canvas to Qt4 model/view
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This part is more complex to do. Also, i think that we must use GraphicsDImgView here, but we need more
investigations. This is the core image editor canvas view implementation. The best way will be to do something 
common between RawPreview, ImageRegionWidget, and Canvas, as an intermediary class down than GraphicsDImgView including
shared methods used these 3 sub-classes...

Note : Canvas has never been ported to PreviewWidget, dur to lack of time, but in past i planed to do it. All API are very similar.
