Repeating banner in Safari and Firefox

[ahzaz]

Opening links from the iframe adds a new banner for each request.

[ahzaz]

IsAlreadyFramed does not work correctly for Safari and Firefox as the Sec-Fetch-* headers are not supported.

The refererURL.Path == r.URL.Path makes it so that moving to different URL on the same host adds the banner again.

would refererURL.Host == r.Host be sufficient to detect if the request is coming from the page served by proxy?

[ahzaz]

Raised a PR#79 for this