i18n: zh_CN locale support

`CONFIG += embed_translations` is used.

main.cpp

@@ -1,15 +1,22 @@
 #include "mainwindow.h"
 #include <QApplication>
 #include <QCommandLineParser>
+#include <QTranslator>
 #include <QUrl>
 
 int main(int argc, char *argv[])
 {
     QApplication a(argc, argv);
 
+    // since we did `CONFIG += lrelease embed_translations`...
+    QTranslator translator;
+    translator.load(QString("PineapplePictures_%1").arg(QLocale::system().name()), ":/i18n/");
+    a.installTranslator(&translator);
+
     // parse commandline arguments
     QCommandLineParser parser;
     parser.addPositionalArgument("File list", QCoreApplication::translate("main", "File list."));
+    parser.addHelpOption();
 
     parser.process(a);