Split this project between the API and Hub

[dartiss]

What problem does this address?

The original Trac request for was for the API, with the idea that anyone could write something like the Hub.

The Hub works great as a demonstration piece, but I can imagine that it may be this component of the project that could hold up with it being implemented in Core - the API less so.

What is your proposed solution?

Split the project into 2 - one the for API and one for the Hub, with the target to get the API implemented pushed into core, and the Hub as a bonus if it is.

This also resolves other questions about other notification implementations (e.g. Jetpack Notifications), as the implementation is something that they can hook into it as soon as possible, and may push then to display all notifications (not just their own), immediately giving up other options to users.

Please confirm that you have searched existing issues in the repo.

Yes