butterflies: fixed population calculation bug and cleanups

src/modules/butterflies/CMakeLists.txt

src/modules/butterflies/butterflies_actions.c

src/modules/butterflies/butterflies_actions_setup.c

src/modules/butterflies/butterflies_actions_setup.h

src/modules/butterflies/butterflies_dispersal.c

src/modules/butterflies/butterflies_dispersal.h

src/modules/butterflies/butterflies_generations.c

src/modules/butterflies/butterflies_initial_population.c

src/modules/butterflies/butterflies_initial_population.h

src/modules/butterflies/butterflies_main.c

src/modules/butterflies/butterflies_overlays.c

src/modules/butterflies/butterflies_paths.c

src/modules/butterflies/butterflies_paths.h

src/modules/butterflies/butterflies_populations.c

src/modules/butterflies/butterflies_populations.h

src/modules/butterflies/butterflies_scale.c

src/modules/butterflies/butterflies_scale.h

src/modules/butterflies/butterflies_stats.c

src/modules/cats_test_module/register_module.c