Improve widgets with settings

The following should be done!
1. There should be a more generic base (not a widget) that will have a unique string as a key.
2. InitAndShow method will be dropped. Instead, there will be a method showIfVisible (only for widgets) as well there will be QTimer:;singleshot called from the constructor, that will initialize key and necessary variables. Another way is to calculate the corresponding string each time. To skip a calculation there can be a flag, that will mark that a new calculation is not needed.