Allow setting classes on list elements

Problem/Motivation

It would be useful for styling if one could configure "Custom classes" for the list element, ul or ol. Currently, custom classes can only be configured for the content itself. This means that these classes cannot set styles like list-style.

Proposed resolution

Add a "Custom classes" configuration for the list element.

Remaining tasks

Implement.

User interface changes

New configuration control.

API changes

None.

Data model changes

None.