If a mail is sent to a domain alias domain and rejected, mailcow does not currently store the mail in quarantine.
This commit adds domain alias handling to the reject code and should fix this behavior.
Also added displaying of recipient addresses into the quarantine mail dialog to be able to see what mail address was "leaked".
[Web] Add system mails (send mails to all mailboxes via LMTP)
[Web] Allow to add more administrators
[Web] Fix domain administrator editing
[Web] Remove some foreign keys
[Web] Remove username from API
[Web] Remove more .php extension from code
[Web] More minor fixes
