Widget: add the _classes method. Fixes #7053: Ability to customize style-related CSS classes
Tabs: use the _classes method. Fixes #7053: Ability to customize style-related CSS classes
Dialog: use the _classes method, deprecate dialogClass. Fixes #7053: Ability to customize style-related CSS classes
Accordion: use the _classes method. Fixes #7053: Ability to customize style-related CSS classes
Autocomplete: use the _classes method. Fixes #7053: Ability to customize style-related CSS classes