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/icore.cpp

@@ -561,6 +561,11 @@ QStatusBar *ICore::statusBar()
     return m_mainwindow->statusBar();
 }
 
+InfoBar *ICore::infoBar()
+{
+    return m_mainwindow->infoBar();
+}
+
 void ICore::raiseWindow(QWidget *widget)
 {
     if (!widget)