Change possible_hoppings -> HoppingKind in tutorial

doc/source/images/ab_ring.py.diff

doc/source/images/graphene.py.diff

doc/source/images/quantum_well.py.diff

doc/source/tutorial/ab_ring.py

doc/source/tutorial/closed_system.py

doc/source/tutorial/graphene.py

doc/source/tutorial/quantum_well.py

doc/source/tutorial/quantum_wire_revisited.py

doc/source/tutorial/spin_orbit.py

doc/source/tutorial/superconductor_transport.py