Remove the redirect_with_whitespace redirect factory block

- This was a hangover of a previous implementation of #16 that I only
  noticed post-merge.
Rename furl_request_spec to short_url_request_spec to match the model

- The naming inconsistency initially confused me when completing #16.
- Fix a small typo in the description of a test.
Merge pull request #17 from alphagov/remove_some_redundant_code_and_tidy_up_filenames

Remove some redundant code and make file names consistent