Make JFormFieldCheckboxes and JFormFieldRadio subclasses of JFormFieldList so that there is only one implementation of getOptions().
New class JFormOption and assorted option-type classes to be used to generate lists of options based on the <option/> xml element.
Other related changes to JForm and JFormHelper.
Affected files now comply with Joomla PHPCS standard.
the 'options' rule now works with the new options system
JFormRuleOptions passes PHPCS
Standard option type can flag options as 'checked' - only affects checkboxes.