Add missing require to DataSetsController

This was causing occasional errors in dev.  Given this class references
this lib, it should be required here.
Merge pull request #97 from alphagov/fix_missing_require

Add missing require to DataSetsController
Restructure places API integration tests.

Structure it so that it's clear what operations the API supports.

This includes placeholders for the full dataset requests (currently in
cucumber), and the authority-bounded requests (not yet implemented)
Migrate integration tests for loading full data set

Migrate them from cucumber to regular integration tests.  This keeps
these tests together in one place... which is nice.
Add pending tests for authority-based lookup.
Add location_match_type to Service model.

To indicate how places for a given service should be matched.
Add snac field to Place model.

The local_authority lookup type will match on this.
Move location lookup logic out of controller

This will make it easier to test and to add the lookup by local
authority functionality
Add MapitApi method to fetch snac for a postcode
Return places in district for local_authority services