Added utility method to convert timestamps to DateTime.
Added test for TimestampToDateTime. It passes.
RealTimeDataEventArgs now carries with it the AssignedID of the request
that caused this data stream to start.
RealTimeDataRequest now has a unique AssignedID that is set at the
RealTimeDataBroker.
Setting AssignedIDs and keeping track of the requests.

Also added saving data to local storage when the SaveToLocalStorage flag
is set.
Testing of saving to local storage.
Added an additional method to IDataStorage, adding a single bar
asynchronously.
The IB client now keeps track of AssignedIDs for real time requests.
Simulated data source keeps track of Assigned IDs.
Small fix.