Bug 1076706 - [Smart Screen][Home] Implement card listing and launching function

Please review only the commit of Bug 1076706, because the base (bug 1076702) has not landed yet

https://bugzilla.mozilla.org/show_bug.cgi?id=1076706
nit: the comment is saying "serialize", so maybe you should move `_serializeCard` up, so these comment is right next to the function declaration?