Notifications that are of the same type but are separated by a groupable
notification of a different type are now considered groupable. For
example:
favorite 1 (status 1)
reblog 1 (status 1)
favorite 2 (status 1)
reblog 2 (status 1)
mention 1
reblog 3 (status 1)
will be grouped into:
favorite 1, 2 (status 1)
reblog 1, 2 (status 1)
mention 1
reblog 3 (status 1)