#1727 Unbinder: handle beans with collections and arrays of other beans

Fix for #1727:

http://play.lighthouseapp.com/projects/57987-play-framework/tickets/1727-unbinder-fails-when-serializing-bean-with-collection-of-other-beans

This fix changes way that collections are unbinded. They no longer will be serialized as `data.collection=[val1, val2]` but to `data.collection[0]=val1&data.collection[1]=val2`.

Let me know if you think it might break something.