Call ImplicitRegistrator fails if coordinate_tensor is None

[kaftanski]

There is an "Unresolved attribute reference 'make_coordinate_slice' for class 'ImplicitRegistrator'" from the following line:

IDIR/models/models.py

Line 23 in 9ab3ccf

coordinate_tensor = self.make_coordinate_slice(

Removing the self and importing make_coordinate_slice from general solves the issue.

Thank you very much for your great work!