Gracefully handle the case where the machine manager is requested to
delete the last machine in Cura. In this case, instead of deleting
everything of this machine and still keep it as an active machine,
the machine manager will set the active machine to None.
The QML files which depend on the active machine were changed to
properly handle themselves when there is no active machine.
CURA-7454
This widget can't set its width to the width of its children, since its children anchor to its right-hand side which depends on the width.
This fixes the following warning in the log:
2020-03-20 14:25:20,351 - WARNING - [MainThread] UM.Qt.QtApplication.__onQmlWarning [406]: file:///home/trin/Gedeeld/Projects/Cura/plugins/PrepareStage/PrepareMain.qml:16:5: QML ActionPanelWidget: Binding loop detected for property width
Done during Turbo Testing and Tooling.
Fixes the following QML warning in the logs:
2020-03-20 14:02:13,482 - WARNING - [MainThread] UM.Qt.QtApplication.__onQmlWarning [406]: file:///home/trin/Gedeeld/Projects/Cura/resources/qml/PrintSetupSelector/Recommended/RecommendedSupportSelector.qml:125:13: Unable to assign [undefined] to int
Instead it now assigns the first extruder before a printer has been created. The first extruder also doesn't exist yet at this point, but this doesn't really matter because there is no interface to show yet at this point.
Done during Turbo Testing and Tooling.
