[FEATURE] #5098 Switch seminars to SwiftMailer

Change-Id: I48230d89429276d5f74e55514371f137a82e5db9
Reviewed-on: http://review.typo3.org/32488
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>