Refactor VCR usage

Currently we are using hand-rolled VCR cassettes which are programatically loaded on a test-by-test basis.

Since this approach was implemented the public_website JSON API is in production so this PR is to use pre-recorded interactions from this in our cucumber features.

Something which could maybe do with some discussion is [features/support/world/action_plans.rb](https://github.com/moneyadviceservice/frontend/blob/929fd672e330ed5d3b490f74808e304c7179a90a/features/support/world/action_plans.rb) and [features/support/world/articles.rb](https://github.com/moneyadviceservice/frontend/blob/929fd672e330ed5d3b490f74808e304c7179a90a/features/support/world/articles.rb). The values in these files were taken from the content on public_website and their format is simply the first thing that worked and half made sense.