Redefine the concept of manager

[StephaneCapponi]

I do think that the term Manager and Hook are not really relevant with the nature of Socon and for everyone else. A Manager should be rename a ServiceManager and a Hook as a Service.

The manager of all Manager should be called a ServiceManagerRegistry,

This ticket is kind of part of the #24 ticket which is the rework of the readme and a part of the documentation. Socon is a Microservice framework and class naming should make sense.