Ensured no duplicate people on ministerial list

I've used Tekin's RolesPresenter which contains helpers to ensure we
have a unique group of people. This class is really a domain class
rather than forming part of the presentation layer: it's a good
representation of a sub-group of roles for an organisation.

This has radically simplified the `ministers_by_organisation` method in
the `MinisterialRolesController` and removed the need for the select
workaround.
Ensure no duplicate people shown in whips section

Propagate the changes made in the previous commit to the whips section,
using the RolesPresenter to show the person information.
Fix first published at label for import documents

Imported documents need a first published at date to be set. Where as
new or edited documents need exectly the inverse.

https://www.pivotaltracker.com/story/show/45484805
Data migration to add/delete more locations

Adds Chad and Mauritania and removes some duplicates, as outlined on
https://www.pivotaltracker.com/story/show/45164823
Merge pull request #316 from alphagov/add-new-world-locations

Data migration to add/delete more locations

https://www.pivotaltracker.com/story/show/45164823
Merge pull request #314 from alphagov/speed-first-published

Fix first published at label for import documents

https://www.pivotaltracker.com/story/show/45484805
Merge pull request #312 from alphagov/remove-duplicate-people-entries

Remove duplicate people entries

https://www.pivotaltracker.com/story/show/45673943