Additional closing modal methods

[laurenceberry]

Adds the option to close the modal using the browser back button and by clicking off the modal itself.

[gdkraus]

Thanks. I'll take a look at the browser history code. As for the clicking on the overlay, is that the expected behavior when clicking on it - that it should close? I'm not sure and I haven't seen that discussed anywhere.

[lectrotext]

So the difference is non modal vs modal.
A modal element does not allow focus to be lost (ie - clicking off the modal). A modal can only be dismissed by submitting or canceling.
A non modal allows the window to be dismissed when focus is lost.