Split most of HorizCoordSys's code into subclasses

[cwardgar]

HorizCoordSys is trying to do too much: it's handling projection, latLon1D AND latLon2D CRSs. We should break some of the code into HorizCoordSysProj, HorizCoordSysLatlon1D, and HorizCoordSysLatLon2D subclasses. HorizCoordSys might then become an interface or abstract class with common method declarations/definitions.