some widget work and superhero pick interface
	modified:   card_selector.py
	modified:   cards/card_constraint.py
	modified:   game_setup_state.py
	modified:   gui/__init__.py
	new file:   gui/checkbox.py
	modified:   gui/gui_state.py
	new file:   gui/images/checkbox.png
	new file:   gui/images/checkbox_checked.png
	modified:   gui/textbox.py