Add filter form to the context.

        TODO: Currently we construct the filter form object twice - in
        get_queryset and here, in get_context_data. Will need to figure out a
        good way to eliminate extra initialization.

def get_context_data(self, **kwargs):
        """
        Add filter form to the context.

        TODO: Currently we construct the filter form object twice - in
        get_queryset and here, in get_context_data. Will need to figure out a
        good way to eliminate extra initialization.
        """
        context = super(FilterFormMixin, self).get_context_data(**kwargs)
        context[self.context_filterform_name] = self.get_filter()
        return context