GitLab

Removed NIFTy 2 files that have not been ported so far.

Adapted imports and setup.py to changes.

propagator_operator still not working to full extend.

Removed nrow, ncol, ndim from operator class.
Made a tomography demo.
Fixed hashing of spaces and fft cache.
Fixed two bugs in the los_response line_integrator.

Resorted the packages and the import structure.

-> Many minor and major bugfixes
-> Reworked indexing (now works with negative step sizes, too)

Updated the naming of domain, codomain, target and cotarget in the spaces, fields and operators.
-> The propagator_operator is now 3 times faster