Now that we have campaign fallback, when a campaign declines to show a banner, another campaign may take the pageview and may show one. The internal API functions for this are called cancelBanner(), but this name no longer seems very clear, given the new process. Something better would be failCampaign() or cancelBannersForCampaign().

Also, the term "banner cancelled" is repeated further downstream in the data pipeline.

We should probably update the function names and terms used in the data pipeline, while maintaining backwards compatibility for both.