Allow user to control how items in a checkbox menu are rendered

[lenormf]

Is your feature request related to a problem? Please describe.
If a user doesn't want to render items in a checkbox menu as [?] - …, they have to override the entire _draw method in CheckBoxMenu.

Describe the solution you'd like
Maybe passing a format string to the CheckBoxMenu constructor that allows controlling colours, weight, characters etc. or a callback that should call a wrapper to _renderer.draw_text() directly.