Initial version of Notifications fetch
Use timestamps to find unread tickets

Instead of a helper boolean
Use comments directly to detect new notifications
Directly fetch tickets by notifications

and not the notifications themselves
Drop the unread test

There is no explicit operation for marking tickets as unread. Ticket are
now implicitly unread by the comment createtAt timestamps.
Fix Ticket#addComment(...) return value

to be the comment

Also refactor triggerUpdate to Ticket#triggerUpdate(...)
Assert return value from the read api

It's now the Notification object