cubicweb #3799043 separate *server activites* from the *repository* [open]

A server is a server is a server. HTTP, or still zmq-pickle.

The repo should provide the necessary abstractions to:
* establish authenticated connections (through which we can manipulate data),
* anchor services,
* maybe declare Tasks to be performed.

The repo should look like a simple, lightweight object, buildable at will from a configuration object. It should not need to be thread safe or be host to the vreg (though it might need it).

done in<not specified>
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