Cleanup code to work better with newer Python

b_asic/GUI/about_window.py

b_asic/GUI/arrow.py

b_asic/GUI/drag_button.py

b_asic/GUI/main_window.py

b_asic/GUI/port_button.py

b_asic/GUI/properties_window.py

b_asic/GUI/select_sfg_window.py

b_asic/GUI/show_pc_window.py

b_asic/GUI/simulate_sfg_window.py