Show child orgs under non-ministerial departments

Some non-ministerial departments have child organisations. These need to
be displayed.
Remove un-needed columns from worldwide organisation.
Merge pull request #289 from alphagov/child-org-index

Show child orgs under non-ministerial departments

https://www.pivotaltracker.com/story/show/45251585
CSV files don't have MIME::Types entries

This causes this check to error out unless we catch it, since it's an
empty array rather than nil.