QmlJS: Show semantic messages on request.

* Add 'Run Checks' action (Ctrl-Shift-C) to perform checks on
  all projects.
* Add 'QML Analysis' build issues category to separate
  clear errors from semantic analysis results.
* Disabled automatic updating of analysis results.

Change-Id: I4c948b1bd39f55655073e56c5e3ca7837f727665
Reviewed-on: http://codereview.qt.nokia.com/2850
Reviewed-by: Leandro T. C. Melo <leandro.melo@nokia.com>
Reviewed-by: Fawzi Mohamed <fawzi.mohamed@nokia.com>

src/plugins/qmljseditor/qmljseditorplugin.h

@@ -99,6 +99,7 @@ public Q_SLOTS:
 
 private Q_SLOTS:
     void currentEditorChanged(Core::IEditor *editor);
+    void runSemanticScan();
 
 private:
     Core::Command *addToolAction(QAction *a, Core::ActionManager *am, Core::Context &context, const QString &name,