Prevent layout blowing up with no logged in user

This currently causes the failure page to blow up because current_user
is nil.
Merge pull request #53 from alphagov/green_is_more_soothing_than_red

Green is more soothing than red.
Add integration test for layout behaviour when signed out
Use `bundle exec` with `rake`

Update README.md to use `bundle exec` when executing rake to prevent errors due to incompatible versions of rake.
Merge pull request #52 from alphagov/fix_layout_error

Prevent layout blowing up with no logged in user
Add in a step sequence for getting the app running

- It took me a while to get up and running so I thought I'd add some copy and paste love to the readme
Add in links to sample files in readme