BUG: Fixing GetGlobalExtent() method to handle multiple layers with multiple srs (in this case all extent are reprojected to the srs of the first layer, which is returned by the method)

ENH: add method in the pixelDescription action handler to disable coordinates to placename computation

BUG: OGRDataSourceWrapper::GetProjectionRef() does not actually return the projection ref, this property is owned by each layer

ENH: Adding background and foreground value to rasterization filter, as well as a flag to deactivate the buring of an attribute