New GeoSpace model

• New GeoSpace model, which is just a singleton instance with no properties.
• New SpaceModelTests tests, with basic init and surrogate tests.
• Added GeoSpace.h/.m and SpaceModelTests.h/.m to the project file.
	» Added by hand, so there's a good chance it won't work when opened in Xcode.  And a slight chance that it will (though Xcode will probably renumber/reorder things.)