Feature Request - Handle onbeforeunload

[gfranko]

We need to handle the situation when a user leaves a particular page and the window.onbeforeunload() method does not seem to be called with the router.

A possible solution would be to patch navigateAction.js to check if there is a window.onbeforeunload() method defined on the window, retrieve the string value from it, and then call window.confirm() with the appropriate string.

Thoughts?

[redonkulus]

This was fixed by #19