Move preference dialog to separate file

b_asic/GUI/__init__.py

b_asic/GUI/main_window.py

b_asic/architecture.py

b_asic/codegen/testbench/test.py

b_asic/codegen/vhdl/__init__.py

b_asic/codegen/vhdl/architecture.py

b_asic/codegen/vhdl/common.py

b_asic/codegen/vhdl/entity.py

b_asic/core_operations.py

b_asic/gui_utils/about_window.py

b_asic/gui_utils/color_button.py

b_asic/gui_utils/icons.py

b_asic/gui_utils/plot_window.py

b_asic/logger.py

b_asic/research/interleaver.py

b_asic/resources.py

b_asic/schedule.py

b_asic/scheduler_gui/__init__.py

b_asic/scheduler_gui/_preferences.py

b_asic/scheduler_gui/axes_item.py