Utils: Rework CheckableMessageBox

Remove function overloads, thes are hard to read, to use and to extend.
I'd even argue this should be a plain default ctor and a few setters +
exec(), pretty much like Process::start() nowadays.

Move "decider" magic into a structure that can be filled ad-hoc outside
checkablemessagebox.cpp paving the ground for:

...removing  aspect dependency from CheckableMessageBox, Instead, add a
convenience function to BoolAspect.  Arguably, the latter is not needed
and could be done on the user side.

Use pointers instead of mutable references for in-out parameter.
Makes the "specialness" visible on the user side.

Pass ICore::settings() centrally as done elsewhere to reduce line noise
on the user side.

Change-Id: Ibb366353d1ea35401723fd05ce05672617a0a8fd
Reviewed-by: Marcus Tillmanns <marcus.tillmanns@qt.io>

src/plugins/coreplugin/coreplugin.cpp

@@ -148,6 +148,7 @@ bool CorePlugin::initialize(const QStringList &arguments, QString *errorMessage)
     Theme::setInitialPalette(theme); // Initialize palette before setting it
     setCreatorTheme(theme);
     InfoBar::initialize(ICore::settings());
+    CheckableMessageBox::initialize(ICore::settings());
     new ActionManager(this);
     ActionManager::setPresentationModeEnabled(args.presentationMode);
     m_mainWindow = new MainWindow;