Modify description on organisations of type other

* Modification to describe organisations of type ‘other’ without
reference to the word ‘other’.
* Addition of a helper method to include the organisation’s parental
and child relationships in its description.
* Supporting tests to ensure organisations are described correctly.
Use helper method to describe organisations

Use of the additional helper method to describe the organisation, with
its parental and child relationships.
Refactor helper method

Refactor helper method for description of organisation’s parental and
child relationships
Merge pull request #1913 from alphagov/fix-organisation-relationship-description

Modify organisation description with parent and child relationships