Changed AddBackendEvent() in ResultClasses to allow the option to not update
the backend progress. This allows the BackendUploader to log the act of starting
an upload without changing the backend progress. The backend progress is now
handled by a new class, FileProgressThrottler, which will determine the transfer
rate of all uploads currently in progress.
This class also handles throttling the upload streams. The algorithm will try
to decrease or increase the streams throttle rates as appropriate by changing
the value based on the over/under amount or based on a percentage to prevent
throttling one stream directly to zero.
Kenneth Skovhede