Minor bugfix and change to allow testing.
Modified DataAdditionRequest constructor again.
Wrote a couple of HistoricalDataBroker tests and added scaffolding for
several more.
Data broker now overwrites locally stored data if SaveDataToStorage is
true.
IContinuousFuturesBroker now inherits from IHistoricalDataSource.
Changes to allow mocking of the ContinuousFuturesBroker in the
HistoricalDataBroker.
IContinuousFuturesBroker now inherits from IDisposable.
Moved the historical data request ending time "present" adjustment to
the broker instead of the server.
Wrote several of the tests in HistoricalDataBrokerTest.