Command for changing organisation slug
Add rake task to change org slug
Define equality for an IndexableNeed as value equality

This is a convenience to help with testing.
Ensure organisation `_id` field properly updated

Need to create a new organisation and destroy the old one, so that the
_id field is updated. The `_id` is expected to match the `slug`.
Update associated needs of a changed organisation

- change the organisation_ids reference
- re-index the need in search
Record need change using appropriate user

This means that if someone looks at the change history of the need
it will be clearer why it was changed
Merge pull request #79 from alphagov/rake-task-to-change-org-slug

Rake task to change org slug