Add PHPMailer Support

Take 2. Now compared to the correct branch *facepalm*.

I added PHPMailer support so users can configure mail delivery through a remote (or local) SMTP server instead of relying on defaults in PHP.ini. 

I do some preliminary checking so users that upgrade and don't copy over the new settings from the settings.php.example won't get errors. It'll simply fallback to using php mail() as it did before.

This is my first PR for nZEDb so I may have done some things that go against normal convention. I plan on contributing a lot to this project in the future so It's important to me I get it right, don't hesitate to give pointers.

Thanks,
KingCat