Add global notification area and use for UI Tour info

Adds a global info bar display above the main window's status bar that
can be accessed via ICore::infoBar().

Replace the blocking "Take UI Tour" dialog by a notification there.

Fixes: QTCREATORBUG-22819
Change-Id: I733f1bfd2d1db0295754ed2e28bb202f927d0edb
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: André Hartmann <aha_1980@gmx.de>

src/plugins/coreplugin/mainwindow.h

@@ -46,6 +46,7 @@ namespace Core {
 class EditorManager;
 class ExternalToolManager;
 class IDocument;
+class InfoBar;
 class JsExpander;
 class MessageManager;
 class ModeManager;
@@ -93,6 +94,7 @@ public:
     virtual QPrinter *printer() const;
     IContext * currentContextObject() const;
     QStatusBar *statusBar() const;
+    InfoBar *infoBar() const;
 
     void updateAdditionalContexts(const Context &remove, const Context &add,
                                   ICore::ContextPriority priority);