Log Message:
Update to 6.2.54. Main changes since 6.2.16:
* Security and bug fixes
* more translations
* Some scenarios and list creation templates for "intranet" use cases were
  made optional: They have been moved into samples/
  https://github.com/sympa-community/sympa/issues/119
  See also "upgrading notes" \ 
(https://sympa-community.github.io/manual/upgrade/notes.html#from-version-prior-to-6250)
  for details.
* Hide full email addresses in archives
* Button for full export of subscribers
* Admin function to bulk unsubscribe
* Delete my account" button
* ARC support (Authenticated Received Chain).