tutorial/source/images: combine latex.py and html.py into defs.py

doc/source/images/1-quantum_wire.py.diff

doc/source/images/2-ab_ring.py.diff

doc/source/images/2-quantum_well.py.diff

doc/source/images/2-spin_orbit.py.diff

doc/source/images/3-band_structure.py.diff

doc/source/images/3-closed_system.py.diff

doc/source/images/4-graphene.py.diff

doc/source/images/5-superconductor_band_structure.py.diff

doc/source/images/5-superconductor_transport.py.diff

doc/source/images/defs.py

doc/source/images/html.py