Persist options override

Hi,

I use different configuration of toasts in my application, and some includes changing how the toast is destroyed (ie: loading indicators gets destroyed without a fadeout and without delay).

The current version of Toastr does not allow this because the options are never saved. I suggest simply persisting them using jQuery's `data` mechanism.

I added both tests and code for this while following (or trying to) existing conventions and coding style, let me know if you see anything wrong.

Thanks,
Jimmy