Update Payment Processing Overview Image

This updates the payment processing image to match the new phrasing "pricing orders".  It also substantially shrinks the height of the image by putting everything on just one line.  (I've been bothered by how large the previous image was.)  Here's a preview: <http://dtrt.org/tmp/en-payment-processing.svg>

If you liked the old image, let me know.  I can restore it and change its text in just a few seconds.