#4 [TODO] Catch exceptions that happen in worker thread

[felixwatts]

When exceptions happen not on the main thread (e.g. in DownloadWorkerPool.RunWorkerCompleted) it seems they are not caught in Main() on the main thread, which allows unhandled exceptions to result in a standard error message to the user. We want to catch these in the catch all in Main() so that the user sees the pp Unhanded Exception Dialog.