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

app/controllers/admin/account_actions_controller.rb

@@ -30,7 +30,7 @@ module Admin
     end
 
     def resource_params
-      params.require(:admin_account_action).permit(:type, :report_id, :warning_preset_id, :text, :send_email_notification, :include_statuses)
+      params.require(:admin_account_action).permit(:type, :report_id, :warning_preset_id, :text, :send_email_notification, :include_statuses, :create_account_summary)
     end
   end
 end