Restructure snlohelper

CHANGELOG.md

README.md

examples/OPA-simulation.py

examples/lnbVsAgs-example.py

examples/plots/.gitkeep

examples/results/.gitkeep

examples/test.py

examples/upconversion.py

pyproject.toml

snlohelper/__init__.py

snlohelper/focus.py

snlohelper/import_snlo_file.py

snlohelper/main_window.py

snlohelper/mix_methods.py

snlohelper/snlo.py

snlohelper/snlohelper.py

snlohelper/two_d_mix_lp.py

snlohelper/two_d_mix_sp.py

snlohelper/utils.py