404 image is 404

[LeifW]

The 404 page, e.g. http://calagator.org/foo
contains an embedded image, http://calagator.org/assets/confused-alligator-sm.png
which itself doesn't exist.

[aeschright]

Alright, this seems to be a casualty of some combination of the Rails engine and Rails 4 migrations. The cleanest option would be to convert this into a dynamic error page that can use the asset pipeline, but I'm inclined to say that the main Calagator gem should continue to have a static page, and we should implement the pretty version on calagator.org. Still requires some cleanup here.