Feature: SERAC - editing possibilities for anonyme reports

**Community discussion about this feature (mandatory)**
Link to where this feature has been discussed.

**Is your feature request related to a problem? Please describe.**
When a SERAC report is created and set to be anonymous, the creator can not edit it afterwards and there is no way to contact him even for moderators.

**Describe the solution you'd like**
For anonymous contributions, display « anonymus contributor » but allow the creator to edit the report, and allow moderators to contact the author (without displaying its identity).

Read the linked community discussion first to understand the agreed behavior for anonymous SERAC reports. Then trace the report editing and moderator-contact entry points; done means an anonymous creator can edit the report and moderators can contact the author without exposing the author's identity.

Written by the indexing model from the issue text.