Add a link to a view or edit a mapping for the page being shown

- This currently linked to transition.dev.gov.uk - when pull request
  transition/191 is merged I'll link it to a non-dev domain.
Change transition.dev to transition.production in the mappings link
Change the mapping link ID to be more descriptive
Actually change the link ID in every place that it occurs

*sigh*
Merge pull request #4 from alphagov/add_link_to_mappings

Add link to mappings