Download progress view is buggy

[mastersign]

• The behavior of the download view is not consistent
• Sometimes it does not show up, sometimes it stayes open
• Old downloads are hanging around in the view
• Sometimes vertical positioning of items in the list is faulty

[mastersign]

Could not recreate the error. A deterministic path to the symptom is required to analyze the behavior.

[mastersign]

There is a possibility, that the downloader was already busy when the setup form was initialized.
Therefore, added UpdateDownloadListVisibility() to SetupForm.InitializeDownloadList().

Need to observe further behavior.

[mastersign]

The error occurs, when the configuration is reloaded by the Core. As a result, the Downloader is recreated, to take possible changes of the proxy configuration into account. But the SetupForm only handed the initial Downloader instance on to the DownloadListControl. If a new Downloader is created at the Core the SetupForm does not react properly.

[mastersign]

In 550b324 the SetupForm hands a newly created Downloader to the DownloadListControl and updates its own registration to Downloader.IsWorkingChanged.