[#1180] Raise 404 for org or group if called wrong

Raise a 404 if a group is called by organization_show
and vice versa.
[#1180] Add tests
Correct syntax
[#1180] Change typos and get the tests to pass
[#1180] *Really* fix tests
Merge pull request #1189 from okfn/1180-groups-orgs-404

[#1180] Raise 404 for org or group if called wrong