ENHANCEMENT: cleanup of composer.json

git-svn-id: https://silverstripe-ecommerce.googlecode.com/svn/modules/payment_dps/trunk@4940 950b781c-c544-efab-2f99-90083ee69683
BUGFIX: better way to reference Email::

git-svn-id: https://silverstripe-ecommerce.googlecode.com/svn/modules/payment_dps/trunk@4941 950b781c-c544-efab-2f99-90083ee69683