Initiatives notifications enhancement

1. Author notifications : - When the initiative title or description has been modified - When an attachment has been added to the initiative - When the initiative has been published or rejected - When the initiative passes a milestone (25 %, 50 %, 75 %) 2. Co-authors notifications : - When a new co-author is authorized to collaborate to the initiative - When the initiative title or description has been modified - When the initiative has been sent to technical validation - When the initiative has been published or rejected - When the initiative passes a milestone (25 %, 50 %, 75 %)