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.
Can you make this throw a sensible exception and/or set the HTTP return code if this parameter isn't set? If you just hit /api/show-tracks right no parameters, it gives you a confusing response.