Add shape of earth 1 and 7

This PR extends `ellispsoid` to handle `shapeOfTheEarth` value `1` and `7`.

This is a precursor to GDT 4/5.
Strictly speaking, yes it will *currently* take an iterable. But we don't need it to take an iterable. And once the MDI changes from #1364 are merged it might *not* take an iterable. So in the interests of progress, how about we just let this kind of thing lie?