broadcast: Factor out broadcast manager into a separate service

[Alan Noble]

It is proposed to factor out the broadcast manager into a separate service called “oceantv” with the eponymous GAE project ID.

To be investigated:
The broadcast UI could either move to the new service or stay behind with VidGrind.

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[Alan Noble]

Keeping Ocean TV as a headless back-end (without a GUI) seems attractive.

There would be a single entry point, /checkbroadcasts, invoked by Ocean Cron. Like Ocean Cron, the Ocean TV service would be configured to run as a single instance to avoid multiple instances interfering (which is possible with the current implementation).

Broadcasts would still be configured via VidGrind’s Admin/Broadcast UI. There are a couple of possibilities for notifying Ocean TV of config changes:

1. Upon saving a broadcast from the UI, VidGrind would send a POST request that includes the broadcast config as JSON data, or
2. VidGrind would write the broadcast config to the datastore then send a GET request.

FYI, Ocean Cron adopts the latter approach.

All HTTP RPCs should be signed using JWT (as for Ocean Cron).

[Alan Noble]

A third option is that the broadcast config form, while hosted by VidGrind, would post directly to a /config method provided by Ocean TV. However this method is insecure since JavaScript can’t sign the request with JWT.