Upgrade mongoid to 3.1.4 (and update dependencies)

delayed_job_mongoid >= 2 is required for mongoid3 support
database_cleaner >= 0.8 is required for mongoid3 support

mongoid3 no longer uses the mongo driver, or bson
Update mongoid config for new version.
Update index definitions to use new syntax.
Update various small things to new mongoid API

Some querying methods have changed.
Cache is no longer specified at a class level.
Update serialisation of Points to new style

See http://mongoid.org/en/mongoid/docs/documents.html#custom_fields for details.
Fix flakey test.

BusinessSupportScheme.last doesn't guarantee any order.
Redo geolookup to use Mongoid3's feature.

Mongoid now implements geoNear, so we can remove our implementation of it.
Fix place duplication.

Was trying to re-serialise the points from the stored hash (which has
string keys).  Point expects symbol keys.
Ensure that indexes have been created for the test db
Remove commented out code.
Remove legacy test, now covered by unit test
Refactor Place archiving
Bulk insert Places from csv data
Bump mongoid to 3.1.5
Revert to linear geoNear queries

The mongoid3 upgrade work included spherical queries. At the moment we use linear
distance calculations in order to gain 2d index performance.
Merge pull request #57 from alphagov/mongoid3

Upgrade to Mongoid 3