Add unit tests for geopoint exports

[jnm]

None of this appears to have any unit tests:

formpack/src/formpack/schema/fields.py

Lines 241 to 244 in 88c8ba1

	# geo
	'geopoint': FormGPSField,
	'start-geopoint': FormGPSField,
	'background-geopoint': FormGPSField,

We should verify that, upon exporting, these types are split into the conventional columns for _latitude, _longitude, _altitude, and _precision.