[ticket/8558] Add display name in emails from board

PHPBB3-8558
[ticket/8558] Add config in migrations and schema_data

PHPBB3-8558
[ticket/8558] Use only one variable and improve explain string

PHPBB3-8558
[ticket/8558] Fix field length in ACP

PHPBB3-8558
[ticket/8558] Fix operator

PHPBB3-8558
Merge remote-tracking branch 'github-elsensee/ticket/stenudd/8558-2' into develop-ascraeus

* github-elsensee/ticket/stenudd/8558-2:
  [ticket/8558] Fix operator
  [ticket/8558] Fix field length in ACP
  [ticket/8558] Use only one variable and improve explain string
  [ticket/8558] Add config in migrations and schema_data
  [ticket/8558] Add display name in emails from board

Conflicts:
	phpBB/includes/functions_messenger.php