Add option to keep evidence when suspending accounts

Fix #547

When selected, before the account's data is removed, some of it
is denormalized into a separate, symmetrically-encrypted table. In
particular:

- The e-mail
- All IPs used to access the account
- SHA256 fingerprints of all uploaded files
- URIs of accounts followed by or following the account
- URIs of accounts that were invited

config/locales/simple_form.en.yml

@@ -9,6 +9,7 @@ en:
       account_warning_preset:
         text: You can use toot syntax, such as URLs, hashtags and mentions
       admin_account_action:
+        create_account_summary: Retain sensitive information such as access IPs, fingerprints of uploaded files, who was following the account and others
         include_statuses: The user will see which toots have caused the moderation action or warning
         send_email_notification: The user will receive an explanation of what happened with their account
         text_html: Optional. You can use toot syntax. You can <a href="%{path}">add warning presets</a> to save time
@@ -73,6 +74,7 @@ en:
       account_warning_preset:
         text: Preset text
       admin_account_action:
+        create_account_summary: Keep evidence
         include_statuses: Include reported toots in the e-mail
         send_email_notification: Notify the user per e-mail
         text: Custom warning