Rich Notifications : New Post notifications

[ghost]

In addition to Comment notifications, we'd like to vend rich New Post notifications.

With the server-side support in place, we should need to make the following client-side changes:

• Modify service extension to support the notifications of type : new_post
• Modify service extension to set categoryIdentifier to a value allowed by the content extension
• Modify content extension to vend a content view appropriate for that type
• Implement content view appropriate for new_post type

Additionally some FormattableContent work may be necessary to detect and/or add the banner image