Includes with titles should have an id for the heading

[bernhold]

We can generate an id for each heading by slugifying the text of the heading. I've done this in _includes/_events/events-list.html. We should do it in others.

[bernhold]

A good default would be to slugify the header content. Still useful to accept an argument to override it.

[bernhold]

While I still think this is a good idea, there are about 30 includes that have a title or similar parameter that results in an HTML heading. Many already accept an additional parameter for the id, but don't have any default. It would be a lot of work to change and test all of these. And I'm not sure it is worth it. So I now consider this lower priority.