Time To Live Indicator for toasts

Add an optional progress bar to toasts to indicate time to live.  This is related to [Issue 188](https://github.com/CodeSeven/toastr/issues/188)
Toastr.scss seemed to be a direct copy of toastr.css (which itself is generated from toastr.less), but it had those few differences. I assumed the differences were not intentional, so when I copied toastr.css to toastr.scss, I allowed the differences to be fixed.

If for some reason you want the scss media queries to be different from the less and css, or if you think it doesn't belong in this pull request, I can change it back.