PictureItemGL::setRotation: Remove unnecessary code
PictureItemGL, PictureItemRaster: Merge rotation calculation code to PictureItemData::setRotation.

Move image size values to PictureItemData (getImageSizeOriginal() and getImageSizeTransformed()).
Add PictureItemData::setImageSize.
Add PictureItemData::setWidgetSize. Remove widgetSize arguments for rest of methods.
PictureItemData: Rename updateSize to updateOffsets
Move duplicate code from PictureItemRaster::setZoom, PictureItemRaster::setRotation, PictureItemGL::setRotation and PictureItemGL::setZoom to PictureItemData::updateSize.
PictureItemRaster: Update paintEvent logic
Move code from PictureItem::afterPixmapLoad to new PictureItemData::resetImagePosition method.
PictureItemData: Add getBoundingRect method and declare m_boundingRect protected.
PictureItemData: Declare pointToOrigin as protected
Add tests for PictureItemData