added mailer component

Added Mailer component, wrapper over SwiftMailer.
i'm not fan of this namespace : your main class is \Phalcon\Mailer\Mailer() ...

the namespace could be Mails (as we have Assets, Models, Events)
and your main class could be called : 
\Phalcon\Mails\Manager()

as it is used to manage messages (send them)

and as we have Assets / Models / Collections / Events ... managers