Fix the event identifier in the EvtSelector

• In order to compute properly if a person start / end in the given period, the method _active_period have been introduce in the EvtSelector .
• The method determines the start (end) date(s) for person associated to an event, to a domain and to a team. The algorithm concatenate the different steps in which parameters like fte can change.
• In the current implementation the event identifier is force to People.
• This wrong since the selector can be applied to many different event. In addition, it should not depends on the application.
• In order to fix it, the event identifier has to be extract from the configuration of the list or metrics.
• One can imagine to modify the database schema for list and metric adding a field id_event