Add clearToast to service

[sunilastudillo]

Need a clear(id) method added to ToastyService. I know there is clearAll() method but I need to be able to clear a single toast from code.

Example:

I'm using a toastyService.wait() toast to display a wait message to the user. The relevant configuration for this toast is:
toastOptions = {
...
showClose: false,
timeout: 0,
...
}

This allows the toast to remain on the screen indefinitely. Now when certain conditions are met, I want to be able to remove that wait toast (and only that toast).

[akserg]

Added in 1.8.0