Cloudinary

Added in Cloudinary functionality. Summary of changes required:
* Added carrierwave and cloudinary gems to Gemfile
* Added required JS libraries
* Added avatar string to organization model (contains url to image on cloudinary)
* Added image browsing to organization registration form
* Replaced stock Salvation Army image with organization's cloudinary image

NOTE: I didn't commit the yml file that contains our cloudinary API keys to source control. I've added this file to gitignore so that we don't accidentally commit it. I will supply this separately to Rodrigo/Serena.