Tweak organisation importer to use document IDs.

Unlike the slug, they're indexed, so we're not doing a collection scan
on each lookup.
Move need_search_result_test.rb to correct directory
Add an "in_scope" boolean field to Need

This adds a new boolean field to Need, "in_scope", which is used to
indicate whether a need is in scope for GOV.UK.

Right now, we only want to be able to mark a need as out of
scope, as there will be future work to add a workflow for deciding that
a need should be in scope on GOV.UK. To reflect this, the in_scope field
can only be nil or false at the present time.

The in_scope field is indexed in search so that it is returned as part
of the need list view.
Merge pull request #33 from alphagov/mark-need-as-out-of-scope

Add a new in_scope field so that Needs can be marked as out of scope
Index organisation names.

We're often pulling these out using the `in_name_order` scope, so it's
sensible to maintain an index to avoid sorting them every time.
Index the organisation IDs on a need.

When we're querying the need API for all needs related to an
organisation, we shouldn't have to scan through all the needs to find
the ones we want.
Order by Mongo ID rather than the `need_id` field.

We're declaring these to be the same thing when we create the need, so
there shouldn't be any functional difference, but the internal document
ID is automatically indexed by MongoDB.
Merge pull request #34 from alphagov/indexing

Indexing
Merge branch 'master' into merging-duplicates

Conflicts:
	app/models/need.rb
	app/presenters/need_presenter.rb
	test/unit/presenters/need_presenter_test.rb