Adding postback after payment redirection (bug 936134, 936139)

https://bugzilla.mozilla.org/show_bug.cgi?id=936134
https://bugzilla.mozilla.org/show_bug.cgi?id=936139
Merge branch 'master' into 936132-postback
Merge pull request #347 from davidbgk/936132-postback

Adding postback after payment redirection (bug 936134, 936139)