Populate world location with the current users

When creating a new edition it should have the current users location
pre-poulated. This will save selecting it every time you create a new
edition.

https://www.pivotaltracker.com/story/show/48759213
Merge pull request #537 from alphagov/default-location

Populate world location with the current users

https://www.pivotaltracker.com/story/show/48759213