Provide a dialog for the editor settings

[peter88213]

To set font, margins, line spacing, colors etc.

These are the settings to be edited (namespace: EditorWindow class):

        manager.kwargs[ed_color_bg_bright]  # 'white'
        manager.kwargs[ed_color_fg_bright]  # 'black'
        manager.kwargs[ ed_color_bg_light]  # 'antique white'
        manager.kwargs[ed_color_fg_light]  # 'black'
        manager.kwargs[ed_color_bg_dark]  # 'gray20'
        manager.kwargs[ed_color_fg_dark]  # 'light grey'
        manager.kwargs[ed_font_family]  # 'Courier'
        manager.kwargs[ed_font_size]  # 12
        manager.kwargs[ed_line_spacing]  # 4
        manager.kwargs[ed_line_width]  # 600
        manager.kwargs[ed_paragraph_spacing]  # 4
        manager.kwargs[ed_margin_x]  # 40
        manager.kwargs[ed_margin_y]  # 20