Allow "orchestrator sponsorship" of specific streamers

We have this right now:

```
-pricePerBroadcaster list of price per broadcaster or path to json config file. Example: {"broadcasters":[{"ethaddress":"address1","priceperunit":1000,"pixelsperunit":1},{"ethaddress":"address2","priceperunit":1200,"pixelsperunit":1}]}
```

But it'd be nice to be more sophisticated here to allow dynamic "sponsorship" of streams.