Made the ImageTransform node work with the new internal image space.
Replaced an old test image with a new and correct one.
Updated the imagePrimitiveSource node to use the new image space.
Added a constructor to GafferImage::Format that allows an arbitrary box to be used as the display window.
Added the bindings and some simple tests.
Updated the FormatPlug bindings to use the new constructor to allow offset display windows to be serialized too.
Changed the name of the default format.
Added support for display windows with non-zero origins.
Added support for reading and writing images with non-zero origins.
GafferImage.ImageWriter is now able to write out black images of the default format rather than just throwing an exception.
Added test cases for the above.
Modified GafferImage.Reformat to add support for images with negative or offset formats.
Fixed an issue where the output display window would occasionaly be wrong by a pixel.