Image perspective correction

This will take a quadrilateral identifying a perspective skewed rectangle in an image, and warp it back to it's original shape.

Determining the aspect ratio of the original item is still not resolved. The technique I attempted to implement for aspect ratio is outlined here: http://research.microsoft.com/en-us/um/people/zhang/papers/tr03-39.pdf and here: http://stackoverflow.com/a/1222855/327471

This addresses issue #16
If you swap the original numbers back in (uncomment them, and comment out the new quad below), but leave the result image view as "Aspect fit" you will see that these numbers also don't estimate the aspect ratio, they simply warp to the source image's size. 

We could accomplish the same thing be removing the aspect ratio estimation on the new method, if that's good enough.