Remove defunct Samurai gateway
Drop stated/tested compatibility with Rails < 3.2

Until we can unhitch ourselves from Rails train completely, we will
track the severe security Rails maintenance policy (background:
http://weblog.rubyonrails.org/2013/2/24/maintenance-policy-for-ruby-on-rails/).

Technically we're not in compliance with that yet since we do not
support/test against Rails 4.1, but that will come soon.
Fix .travis.yml to refer to correct Gemfile
Remove no longer needed test dependencies
Verify the length/format of the card verification value