Lists: not yet implemented functionality

[berenddeboer]

Lists currently do not support the following:

• [x] List items should ripple.
• [x] Keyboard interaction via up and down keys.
• [x] tabindex should be set.
• [ ] A radio button in a list item cause a double ripple. If you click the radio button, the list item itself should not ripple. Apparently for a checkbox is should ripple (what we're currently doing).
• [ ] Handle left and right arrow if horizontal list. Currently we have no concept of vertical or horizontal, the list is vertical by definition.
• [ ] Possibly need to disable keyboard interaction for nonInteractive lists.

[berenddeboer]

Currently we don't set tabindex when non-interactive, so perhaps that means it never gets keyboard focus.