support single action live streams

[skaes]

It should be possible to have a live stream of a single controller action.

However, creating a live stream for every action is terribly wasteful: it would mean thousands of streams, to which nobody ever listens.

Thus we would need to modify the live stream server and the importer to be aware of which streams are being listened to and calculate the live stream data only for those streams.

Also, the ruby implementation of the live stream wouldn't cut it anymore: we'd need to move to C, with heartbeats and all the shizzle.