Adds the DataTransferTask and DataTransferProgressDisplay classes, which use repurposed logic from the DownloadTask and EtaProgressDisplay classes, respectively. The EtaProgressDisplay class and EtaProgressInfo struct have been removed.
Other changes include:
* DownloadTask: heavily simplified logic by using DataTransferTask as the base class.
* DumpOptionsFrame: implement some additional/experimental changes.
* OptionsTab: update logic to use the new DataTransferProgressDisplay class.
