Windows Qt: Add taskbar progress support

Add support for the taskbar progress indicator on Windows via
QtWinExtras. It is almost as if we're a grown up Windows application.

Change-Id: I378206b49510d4bd08f2437d8e9a1b01bc6f1351
Reviewed-on: https://code.wireshark.org/review/3576
Petri-Dish: Gerald Combs <gerald@wireshark.org>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Gerald Combs <gerald@wireshark.org>