#8 Additional transformation

[vISTe]

Currently, the Transformation plugin only supports flipping (mirroring) an image. However, other transformation may also be added. For example, the ability to rotate the image by 90 degrees would be very useful for images for which direction-based coloring is incorrect (e.g. the center of the corpus callosum is blue instead of red). The ability to create a custom transformation matrix may also be useful.