Strong params

This branch implements strong parameters and rips attr_accessible from our code.

It also gets Cucumber tests up and running. There are some intermittent issues with VCR and an inconvenient command line syntax, but I'm going to fix those. You can run Cucumber specs by running:

`RAILS_ROOT=/rails/root/directory bundle exec cucumber spec/features/feature_file.feature`

To get Cucumber to work, I had to move from a transactional database cleaning strategy to a :truncate one. This slows down rspec tests; I'm also going to figure out how to fix this.