WIDGET_STATE_FOCUSED: new state and it base handling.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
NOT FINISHED: Reimplement focus/unfocus handling in widgets.

TODO: panel, tree, editor, etc.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
(menubar_new): add 3rd visible argument.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>