Fix bug : nbr attempts did not increase
Enable Expose REST Metric API for all selectors

Only WriteEnabledSelectors can expose write REST API (for create subscriptions, and in the future delete subscriptions)
Enable good handling of sent flag on decorated notification for SingleMultiTopicMail
Fix some bugs in Persister statistics methods
Allow to set custom from and subject in notifications
Commit after merge
Issue #22 : add some recipient display name in context
Issue #22 : updated notificators and fix bugs