Revamp MIME Type Browser Ex: Fix includes

Fix include order to respect the Coding Conventions.

Remove QT_{BEGIN,END}_NAMESPACE because these are private Qt macros that
should not be used in the examples.

Task-number: QTBUG-117146
Pick-to: 6.6 6.5
Change-Id: Iba7a4726180ec97d9654ed3b934baca8c1df0b5c
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>

examples/corelib/mimetypes/mimetypebrowser/main.cpp

@@ -4,10 +4,8 @@
 #include "mainwindow.h"
 
 #include <QApplication>
-#include <QScreen>
-
 #include <QCommandLineParser>
-#include <QCommandLineOption>
+#include <QScreen>
 
 int main(int argc, char *argv[])
 {

examples/corelib/mimetypes/mimetypebrowser/mainwindow.cpp

@@ -4,23 +4,18 @@
 #include "mainwindow.h"
 #include "mimetypemodel.h"
 
-#include <QAction>
 #include <QApplication>
 #include <QFileDialog>
+#include <QFileInfo>
 #include <QInputDialog>
+#include <QItemSelectionModel>
 #include <QMenu>
 #include <QMenuBar>
 #include <QMessageBox>
-#include <QPlainTextEdit>
-#include <QSplitter>
-#include <QStatusBar>
-#include <QTextEdit>
-#include <QTreeView>
-
-#include <QFileInfo>
-#include <QItemSelectionModel>
 #include <QMimeDatabase>
 #include <QMimeType>
+#include <QSplitter>
+#include <QStatusBar>
 
 MainWindow::MainWindow(QWidget *parent)
     : QMainWindow(parent)

examples/corelib/mimetypes/mimetypebrowser/mainwindow.h

@@ -4,12 +4,11 @@
 #ifndef MAINWINDOW_H
 #define MAINWINDOW_H
 
+#include <QAction>
 #include <QMainWindow>
 #include <QModelIndexList>
-
-QT_FORWARD_DECLARE_CLASS(QAction)
-QT_FORWARD_DECLARE_CLASS(QTextEdit)
-QT_FORWARD_DECLARE_CLASS(QTreeView)
+#include <QTextEdit>
+#include <QTreeView>
 
 class MimetypeModel;
 

examples/corelib/mimetypes/mimetypebrowser/mimetypemodel.h

@@ -4,10 +4,9 @@
 #ifndef MIMETYPEMODEL_H
 #define MIMETYPEMODEL_H
 
-#include <QStandardItemModel>
 #include <QHash>
-
-QT_FORWARD_DECLARE_CLASS(QMimeType)
+#include <QMimeType>
+#include <QStandardItemModel>
 
 class MimetypeModel : public QStandardItemModel
 {