Make modaless Issuer API call return back to the issuer at the end

[stenington]

Badge earners are better served by being delivered back to the issuer where they can earn more badges at the end of the "push to backpack" flow. Change the Issuer API modaless call to deliver earners back to the issuer either automatically, or based on a "return to" url passed as a call parameter.

[threeqube]

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