2.5.x features

shows, show-schedules, show-preview, show-history-feed, item-history-feed endpoints to the HTTP api to be used via NewscoopAirtimePlugin

These endpoints are needed for airtime pro instances and should be merged to saas branch.
Ah, my bad.  Yeah, maybe this would be better named showTrackListingAction(), and I thought at first it would be better to not make this publicly available since it exposes file ids, but I don't see the harm in making it public since the getMedia() function requires the apiKey anyway.