Retain widget settings through switches and closes

[celeste-sinead]

Overall, the intent is to make it more convenient to switch back and forth between widgets, or to temporarily show and then hide a widget, by not reverting widgets to default settings when doing this. More specifically:

• when a dock is closed, and then a new dock is created, the new dock will have the same widget with the same settings as previously (and this works on a stack if multiple docks are closed)
• when a dock is switched from one widget to another and then back, the initial settings will be preserved
• the above state is persisted in application settings