Batch mailing

Proposal for a batch email sender implementation

I used Try/Success/Failure from the scala library to avoid pulling scalaZ which is a very large dependency.

A possible path to Async batch mailing could be : 
````scala
def sendEmails(emails:Seq[Email])(implicit executionContext:ExecutionContext):Future[Seq[Try[Email]]]={
    import scala.concurrent.future
    future{Mailer.sendEmails(emails)}
}
````

This was not implemented in this pull request.