core: twistd plugin refactoring: initialisation method manage things which must be done once (reactor installation + logging configuration), this method is called when service is created, so we can have the options passed to twistd (necessary to manage logging configuration). The initialisation order is important: for instance, sat_main must be imported after logging initialisation. This refactoring avoid initialisation issue when SàT backend and libervia are both installed as twisted plugins.

<node>
  <interface name="org.goffi.SAT.core">
  </interface>
</node>