ko.observableArray of ko.observables & templates

When a ko.observableArray of ko.observables is bound using the foreach binding, the $data variable refers to the unwrapped ko.observable instead of the observable itself. 
See also [this StackOverflow question](http://stackoverflow.com/q/16522421) and [this fiddle](http://jsfiddle.net/jessevanassen/qRXua/).

This pull request introduces the $item variable within the foreach, which refers to the raw item, which isn't unwrapped if it is an observable. This makes it possible to bind the value of the observable bidirectionally, by using `data-bind="value: $item"`.