Merge Country and OverseasTerritory location types

These are now just to be called "World locations".

This involved considerable noise changing all the factory references to
remove calls out to country etc. in order to clean up.
Merge pull request #384 from alphagov/merge-country-and-territory-types-rebased

Merge Country and OverseasTerritory location types

https://www.pivotaltracker.com/story/show/46713179