Add ability to remove or add 'none' option in buttons block

This patch adds the toggle button.

Thanks, Abdulrahman, for suggesting and patching

1. Creating issue forks → to be able to commit with --author .. I can not see your --author email ( which switched to MR by Drupal.org )

2. Suggesting a better name for the config values in the settings.
Somthing like

• Change none_option_color to show_none_for_color or show_none_option_color
• Change none_option_size to show_none_for_size or show_none_option_size

Welcoming any better readable config names