Document views for updated embed widgets

Move documentation of context out of the template and into the template
file to the ``get_context_data()`` declaration

In the process of documenting various view class methods, I cleaned
up the signature of the ``StoryListMixin.get_story_list()`` method:

* Remove the ``count`` argument as it seems more consistent to slice
  the returned queryset in the calling code.
* Make the ``view_kwargs`` argument default to ``self.kwargs``

Addresses #741