Initial attempt to load all descendants

Recursively going through the subjects looking for subOrganizationOf
Write JSON to the kv store for each organisation
Specify media type to turtle
Rename - -> _
Added task to run the descendant importer
Simple view / service to return POI Descendants
Added tests for OxpointsDescendantsImporter
Updated descendants importer to be generic

Rather than hard coded to be suborg descendants it can follow any
specified predicate.
Fixed typo
Renamed url, view, service to be more specific

Specifying that we return the *organisational* descendants
Merge pull request #61 from ox-it/oxpoints-descendants-task

Oxpoints descendants task