WIP further refactorings #1

Mail_Queue's current public API leaves a lot to be desired.

• use ArrayObject to be able to iterate across the queue more easily
• remove put and implement something like add(Body $mail)
• take a look at the callback implementation
• add fluent interfaces
• add set*() methods for what is public (and do proper validations)

Mail sending

• decouple mail sending
• allow/support different mailers (Zend_Mail, Zend\Mail, Swiftmailer)

Containers

• add a Doctrine container
• research suitable systems for this

logger

• supporting a logger would be nice as well to escalate to syslog, etc.
• figure out if PEAR has something suitable (or use Zend\Log or monolog)