use Rails 3 Mailer API for mailer models and in tests

Instead of calling body with a hash for the view instance variables are
now copied into the view just like in controllers.

Also the syntax for .create_bla and .deliver_bla has changed
to .bla and .bla.deliver.

see http://lindsaar.net/2010/1/26/new-actionmailer-api-in-rails-3