Updated to allow for s3 storage from paperclip.

[JangoSteve]

I updated citizenry to allow for s3 storage from paperclip (for the avatar and logo uploads/import from url). It still uses the filesystem by default (just as before), but now allows the user to easily change it to s3 from the settings.yml.

This would also allow for easier hosting on heroku (see #45), since it's necessary to persist images across deploys.

[JangoSteve]

FYI, deploying on heroku will seem to work without this pull request, but then when you git push heroku, all of your images for people, companies, and groups will be wiped out, breaking all the images on your site.

If you pull this in, then the framework is totally heroku-ready. I'll update the heroku wiki with the 2 steps required to switch to amazon s3 for image uploading after this is pulled in (basically, uncomment a line in the Gemfile and uncomment 3 lines in the app_settings.yml).