Add ability to change the stacking direction

[MichaelPGriffin]

The default behavior appends each additional notification to the bottom of the "stack" of visible notifications.

It would be convenient if there were an way to insert new notifications at the top instead of appending them to the list.

[mansona]

Would you be able to achieve this using CSS and overriding the styles for the notification container? 🤔 now that https://github.com/mansona/ember-cli-notifications/pull/251 has been merged and released it should be much easier to override styles 👍