Write out Tiled version in TMX/JSON "version" attribute

Now we've reached "Tiled 1.0" and this means it is about time that
version attribute starts tracking the Tiled version.

Closes #1416

src/libtiled/maptovariantconverter.cpp

@@ -32,6 +32,8 @@
 #include "tileset.h"
 #include "terrain.h"
 
+#include <QCoreApplication>
+
 using namespace Tiled;
 
 static QString colorToString(const QColor &color)
@@ -49,7 +51,7 @@ QVariant MapToVariantConverter::toVariant(const Map &map, const QDir &mapDir)
     QVariantMap mapVariant;
 
     mapVariant[QLatin1String("type")] = QLatin1String("map");
-    mapVariant[QLatin1String("version")] = 1.0;
+    mapVariant[QLatin1String("version")] = QCoreApplication::applicationVersion();
     mapVariant[QLatin1String("orientation")] = orientationToString(map.orientation());
     mapVariant[QLatin1String("renderorder")] = renderOrderToString(map.renderOrder());
     mapVariant[QLatin1String("width")] = map.width();

src/libtiled/mapwriter.cpp

@@ -177,7 +177,7 @@ void MapWriterPrivate::writeMap(QXmlStreamWriter &w, const Map &map)
     const QString orientation = orientationToString(map.orientation());
     const QString renderOrder = renderOrderToString(map.renderOrder());
 
-    w.writeAttribute(QLatin1String("version"), QLatin1String("1.0"));
+    w.writeAttribute(QLatin1String("version"), QCoreApplication::applicationVersion());
     w.writeAttribute(QLatin1String("orientation"), orientation);
     w.writeAttribute(QLatin1String("renderorder"), renderOrder);
     w.writeAttribute(QLatin1String("width"), QString::number(map.width()));