This commit adds a blue dot next to the "What's New"
link in the admin sidebar if the user has not seen the
new features yet, as a followup to 3e5976f8436255185de556ae165d9d849ac8fb3a
which removed the tab on the dashboard that had this same
functionality.
When the admin visits the "What's New" page they count
as having seen all the features straight away. This could
be something we want to change, but for now this keeps the
same functionality.
