Amend the glossary definition of a mapping
Merge pull request #278 from alphagov/amend_glossary_mapping_definition

Amend the glossary definition of a mapping
Blanket find and replace URI.parse() to Addressable::URI.parse()

- The tests are meant to fail - I'm fixing them in a separate commit
  to avoid quite so many one-line changes.
- If there's a file in here that's not meant to be here, let me know
  and I'll attempt to take it out.
Fix the tests that were failing after d3de9c0e5d

- This makes sure that at least some XSS vulnerabilities are catered
  for, by checking that the path doesn't contain `<script>`.
  `URI.parse` did this for us, but we don't have the luxury using
  `Addressable::URI.parse`, as it is a valid URL according to the RFC
  it uses - see https://github.com/sporkmonger/addressable/issues/141.
- Underscores are also valid according to `Addressable::URI.parse`,
  so change the tests using underscores for invalid data to use curly
  braces for invalid data. Revert the changes in 30b999a that had to
  change underscores to dashes for `URI.parse` to confirm the
  hostnames as valid.