Currently the process of adding a custom image to badge is quite clunky; you have to upload your image to a topic, and then copy the image URL and pasting it in a text field. Besides being clucky, if the topic or post that contains the image is deleted, the image will be garbage-collected in a few days and the badge will lose the image because the application is not that the image is referenced by a badge.
This commit improves that by adding a proper image uploader widget for badge images.
