Port Qt Creator to the new plugin system of Qt 5.

- Add Q_PLUGIN_METADATA for Qt 5, use Q_EXPORT_PLUGIN
  for Qt 4.
- Generate the Json files for Qt 5 from the pluginspec
  files by using a XSLT sheet.

Change-Id: I8653f182ae7d61615971c093df10b84fb06c2172
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@nokia.com>

src/plugins/helloworld/helloworldplugin.h

@@ -42,6 +42,7 @@ class HelloWorldPlugin
   : public ExtensionSystem::IPlugin
 {
     Q_OBJECT
+    Q_PLUGIN_METADATA(IID "org.qt-project.Qt.QtCreatorPlugin" FILE "HelloWorld.json")
 
 public:
     HelloWorldPlugin();