Notifications

[flauc]

We need to build a notifications module that's both standardized and extendable. The idea for the module is to present notifications in real time to a user when specified documents are created, updated or deleted. We also need to consider authentication and we need to consider that the user who triggered the action should not receive a notification about the action.

For example:

1. A user document is created and the user module is configured to receive notifications.
2. I'm logged in as an admin and it wasn't me who created the document.
3. I'm presented with a notification saying User {{key specified as title in the user collection}} was created
4. Clicking on the notification would dismiss it and take me to that user (or a link specified when configuring the collection for notification)

Ideally we would also have a notifications icon with count somewhere in the layout and the notifications table would be filterable by read/unread.