Changed the dropbox url for the portrait image.

The rational here is simple: The thumbnails generated by dropbox are transitory; the intention is for you to always make a request for the thumbnails should you want them. While dropbox will cache them for a long time, they can be deleted at any time. (Or have their url change.) However, the 'download' url is served via their CDN, and is intended as a perma-link to the file. It's url should never change.

This new URL should be faster, more robust, and more inline with Dropbox's api. It has a secondary effect of not limiting images to 200x200px. I have tested and it handles non-square images as you would expect.