Content-Security-Policy handling

[grantat]

Web.archive.org introduced a new Content-Security-Policy for live web leaking into the mementos and memento-damage isn't really handling them. Here is one example:

• http://web.archive.org/web/20040208171032/http://www.deviantart.com:80/

A lot of the images don't return a proper response code and are rendered in the page as empty. This should be affecting damage even though they don't have a proper response code.