New hourly charge

up

1. Broker creates a new HourlyCharge instance h for a variable Rate r on some Tariff t.
2. Broker sends new HourlyCharge to the server
3. Accounting service receives message, looks up Tariff t, and passes message content to t.addHourlyCharge(h) method.
4. Tariff inspects HourlyCharge h to extract Rate ID, looks up Rate, passes HourlyCharge instance to r.addHourlyCharge(h).
5. Rate adds the HourlyCharge h to its rateHistory.

Assumption:Customers do not need to be notified of these updates. Instead, we assume they will autonomously inspect the current and future values for variable rates in the process of running their models.
Open question: Do HourlyCharge notifications get sent to all the Brokers? As individual messages, or bundled? For the moment we assume they are not notified. This is a market-transparency issue. Possibly they should be made public 24 hours afterward.