add gpt.iframeExternalUrl support
add gpt.iframeExternalUrl support

If gpt.iframeExternalUrl is defined, it overrides iframeUrl, and it should be
something like this:

    //your.other.domain/some/server-side-file.php?q=

See readme for more.

brewingcode/ember-google-publisher-tags,brewingcode/ember-google-publisher-tags