[CLEANUP] #4283 Clean up the mailer classes.

Change-Id: Ibfe37ea25851ddb045c172276c16a759491dcfe4
Reviewed-on: http://review.typo3.org/32477
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>