Staging requires registration inversion

[nrhorner]

If skip_transform_inversion = true and staging = 'whole_embryo' for example it fails to find the inverted masks.

Make a check for this

[dorkylever]

Yeah I've ran into this issue when running the test-code as well.

[dorkylever]

I'm going to try implement whole embryo volume labelling using the otsu algorithm that Henrik gave to me a while back. That way you can still the embryos without inversion.