Redirect window to redirect_url if provided

[owenkellogg]

If the invoice includes a redirect_url redirect there two seconds after paid.

Wait redirect_delay milliseconds defaulting to 2000 milliseconds.

[azimgd]

• automatic redirect with countdown when user is paying for invoice
• no redirect when user is browsing the receipt for the second time

[azimgd]

• implement countdown (you will be redirected back to merchant in X seconds)

[azimgd]

• if no redirect there is no countdown
• if no redirect there is done button

[azimgd]

• redirect behaviour should be according to the widget's inclusion type
• if widget is embeded or hosted at anypay, behaviour should change