SMTP Mail - Support for server authentication for "built-in" Send Email to Contact(s)

Some users' SMTP servers require authentication. This is supported in our SMTP PEAR package - but we need to give users a way to configure in civicrm.settings.php.

Implement/document additional smtp params in STMP server section in civicrm.settings.php and modify code to pass these values conditionally in Core/Config.php:

$params["auth"] - Whether or not to use SMTP authentication. Default is FALSE
$params["username"] - The username to use for SMTP authentication.
$params["password"] - The password to use for SMTP authentication.

Will need to trap and return error status msg if auth parm is true and user/pw not defined. Also need to trap and handle invalid auth error from SMTP server.