Add aruba to dependencies

As this is required for running the feature tests.
Put dependencies in alphabetical order
Remove unnecessary options

This test is run on the command line so we do not need a results.html. Also removed this from gitignore as it will no longer be generated.
Re-order Rakefile for clarity
Change task names for consistency

- feature rather than features to match other tests
- integration can be symbol rather than String
Make default rake task feature tests

Eventually this should be unit and feature tests, but there are no unit tests.
Merge pull request #4 from alphagov/fix-feature-tests

Fix feature tests