[TASK] Load swiftmailer via composer

Instead of manually requiring the necessary
swiftmailer information, composer can be
utilized to be included in the regular autoloading
process.

At the same time, typo3/contrib/swiftmailer
is moved into typo3/contrib/vendor which is
maintained by composer.

TYPO3 Instances maintained with composer
will put the swiftmailer library into
Packages/Libraries/.

Resolves: #65950
Releases: master
Change-Id: Ibd57dddf74ed6643fd1f0816517e6bb36d22c3eb
Reviewed-on: http://review.typo3.org/38057


Reviewed-by: Helmut Hummel <helmut.hummel@typo3.org>
Tested-by: Helmut Hummel <helmut.hummel@typo3.org>