- Turn the Quaternion inside a GeoDataCoordinate into a pointer

- Instantiate the Quaternion and initialize it lazily only once
  quaternion() is called
As a result the quaternion is only instantiated for spherical
projections. And it only gets instantiated once the
GeoDataCoordinate object is evaluated for drawing.
This reduces initialization time and reduces the memory footprint
by about 4 MB on average.