Show only one table on the org page, containing sites & extra_sites

- Move into one table following feedback from @fofr, as it is neater.
- For sites that are owned by a different organisation than the one
  the user is looking at, include that information on a greyed-out
  line underneath the site URL.
- Remove `with_mapping_count` site scope that was in use in the
  OrganisationController. It didn't seem to be doing anything.
- Add horrible numbers of spaces to the test - it's interpreting
  indentation as spaces, so the test was failing without line breaks
  or this number of spaces.