Prevent notifications from being too tall and unclosable

Closes #1558

- Adds a wrapping tag around the notification message
- Change tests to look for new wrapping tag

For the fix to work properly, it needs styles from the [0.8 branch](https://github.com/TryGhost/Ghost-UI/commit/b98029911c4695f17cb9d05bc48ca5e8eeb77bf6) of Ghost-UI
Merge pull request #3059 from PaulAdamDavis/1558-notifications-ui

Prevent notifications from being too tall and unclosable