Put images in a single directory

Move the contents of https://github.com/python-pillow/Pillow/tree/master/Images to https://github.com/python-pillow/Pillow/tree/master/Tests/images and update paths as needed.

For https://github.com/python-pillow/Pillow/issues/707.

History is preserved but you need to use the command line like this: 

`git log --follow Tests/images/courB08.pbm`