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.cpp

@@ -365,6 +365,11 @@ QStatusBar *MainWindow::statusBar() const
     return m_modeStack->statusBar();
 }
 
+InfoBar *MainWindow::infoBar() const
+{
+    return m_modeStack->infoBar();
+}
+
 void MainWindow::registerDefaultContainers()
 {
     ActionContainer *menubar = ActionManager::createMenuBar(Constants::MENU_BAR);