revert to devise 3.0.x due to confirmable misbehaviour

as documented here: https://github.com/plataformatec/devise/issues/3009

also update mailer to use letter_opener and also localhost:8080 since
we're mostly using unicorn at this point.
Merge pull request #347 from Skud/devise-bug2

revert to devise 3.0.x due to confirmable misbehaviour