Link the admin1s in admin_unit_global/tropical to their countries, using GAUL codes provided by Catherine (and stored in new table admin_unit_country). Create views on these for use by the application.
Fix admin levels of Canada and Russsia in admin_unit_tropical.
Determine the location's country GAUL code during post-QC.
Disease extent generation: first draft of handling admin1s with no occurrences; refactor code to use a helper.
On AdminUnitReview, replace the classes AdminUnitGlobal/Tropical with the GAUL codes, for efficiency.
First draft of code to update an existing disease extent.
Add tests
Merge branch 'master' into 36-159-disease-extent-generation

Conflicts:
	db/data/data.sql
Fixes following review.
Added missing admin unit GAUL codes from Catherine.
Merge pull request #114 from SEEG-Oxford/36-159-disease-extent-generation

Disease extent generation