Moved the mainwindow examples from qtdoc

Change-Id: I5a11933e86c6c71f68a55e45c7bcfdfc702bf4e6
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>

examples/widgets/doc/src/application.qdoc

@@ -28,6 +28,7 @@
 /*!
     \example mainwindows/application
     \title Application Example
+    \ingroup examples-mainwindow
 
     \brief The Application example shows how to implement a standard GUI
     application with menus, toolbars, and a status bar. The example

examples/widgets/doc/src/dockwidgets.qdoc

@@ -28,6 +28,7 @@
 /*!
     \example mainwindows/dockwidgets
     \title Dock Widgets Example
+    \ingroup examples-mainwindow
 
     \brief The Dock Widgets example shows how to add dock windows to an
     application. It also shows how to use Qt's rich text engine.

examples/widgets/doc/src/mainwindow.qdoc

@@ -28,6 +28,7 @@
 /*!
     \example mainwindows/mainwindow
     \title Main Window
+    \ingroup examples-mainwindow
 
     \brief The Main Window example shows Qt's extensive support for tool bars,
     dock windows, menus, and other standard application features.

examples/widgets/doc/src/mdi.qdoc

@@ -28,6 +28,7 @@
 /*! 
     \example mainwindows/mdi
     \title MDI Example
+    \ingroup examples-mainwindow
 
     \brief The MDI example shows how to implement a Multiple Document Interface using Qt's
     QMdiArea class.

examples/widgets/doc/src/menus.qdoc

@@ -28,6 +28,7 @@
 /*!
     \example mainwindows/menus
     \title Menus Example
+    \ingroup examples-mainwindow
 
     \brief The Menus example demonstrates how menus can be used in a main
     window application.

examples/widgets/doc/src/recentfiles.qdoc

@@ -28,6 +28,7 @@
 /*! 
     \example mainwindows/recentfiles
     \title Recent Files Example
+    \ingroup examples-mainwindow
 
     \brief The Recent Files example shows how a standard File menu can be extended to show
     the most recent files loaded by a main window application.

examples/widgets/doc/src/sdi.qdoc

@@ -28,6 +28,7 @@
 /*! 
     \example mainwindows/sdi
     \title SDI Example
+    \ingroup examples-mainwindow
 
     \brief The SDI example shows how to create a Single Document Interface. It uses a number of
     top-level windows to display the contents of different text files.

src/widgets/doc/src/qtwidgets-examples.qdoc

@@ -139,3 +139,18 @@
 
 */
 
+/*!
+    \group examples-mainwindow
+    \ingroup all-examples
+    \title Main Window Examples
+    \brief Building applications around a main window.
+
+    \image mainwindow-examples.png
+
+    All the standard features of application main windows are provided by Qt.
+
+    Main windows can have pull down menus, tool bars, and dock windows. These
+    separate forms of user input are unified in an integrated action system that
+    also supports keyboard shortcuts and accelerator keys in menu items.
+
+*/