qmlprieview: fix that init language is the chosen one

* removes language feature from preview service
* it is handled by an extra DebugTranslationService until now
* Qt versions without that extra service can not preview
  languages anymore
* Introduce the use of QmlPreviewRunnerSetting. It makes it
  easier to add more properties in the future
* Language needs an extra handling because it needs
  the loadUrl to find existing languages. So we save
  the language to a m_scheduledInitLanguage and emit
  this after the loadFile call happend.

Change-Id: I7f4aec97f7b61d6b290f225282169da594eb9160
Reviewed-by: Marco Bubke <marco.bubke@qt.io>

src/plugins/qmlpreview/qmlpreviewclient.h

@@ -43,8 +43,7 @@ public:
         Directory,
         ClearCache,
         Zoom,
-        Fps,
-        Language
+        Fps
     };
 
     struct FpsInfo {
@@ -64,7 +63,6 @@ public:
     void loadUrl(const QUrl &url);
     void rerun();
     void zoom(float zoomFactor);
-    void language(const QUrl &context, const QString &locale);
     void announceFile(const QString &path, const QByteArray &contents);
     void announceDirectory(const QString &path, const QStringList &entries);
     void announceError(const QString &path);