CheckButton is a generic component based on Button that additionally
takes a *bool variable to manage. When the CheckButton is clicked or
unclicked, it will toggle the bool var and its border style will "stick"
in or out depending on the state.
Checkbox is a Frame widget that wraps a CheckButton and another child
widget, such as a Label. Interacting with the child widget will forward
all of its mouse events to the CheckButton, so that the Label could be
clicked instead of just the box itself.
