Remove unused code

Get rid of QGCView, QGCViewPanel and FactPanel. All messages and dialogs are now handled in the root window.

The Url in custom command widget has been moved to
https://docs.qgroundcontrol.com/en/app_menu/custom_command_widget.html

Signed-off-by: Patrick José Pereira <patrickelectric@gmail.com>

This reverts commit 7e6588f6.

Adding missing qgcView to QGCMapPolygonVisuals instance in SurveyMapVisual.qml

_finalize methods need information which is not available if all you
have is a mavlink_message_t

Also report the current transfer rate in the currently downloading status to help expose regressions in performance.