Use PIL Image everywhere, replace numpy arrays

[aydin-utting]

• We use a mixture of PIL Images and numpy arrays
• The colour channels are BGR for numpy arrays and RGB for PIL images (mostly) and this confusion leads to incorrectly rendered images
• PIL images are probably the better choice, and they are arrays under the hood so it doesn't matter anyway.
• The first place that we render an image is the PDFDocument render_page function which uses numpy arrays. We should replace this with PIL.Image and then propagate that change through to everywhere else.
• We should replace the numpy array functions for cropping and rotating with PIL built in functions like PIL.ImageOps or just PIL.Image methods