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. (The SVG code already handle correct cropping.)
Fixed the edit screen to scale the image like svg.

Now, the character edit page correctly mimics the behavior of the
combatant on the svg grid, when it comes to handling non-square images.
Merge pull request #64 from lordnull/feature-cc-dropbox-url-fix

Changed the dropbox url for the portrait image.