VariableManager: Add support for javascript varibales

Add JsExpander that can be used to register additional functionality
in its qscriptengine and to evaluate expressions.

Register that with the VariableManager, using the "JS" prefix.

Change-Id: I7d8f1ddc3484104f3943685dbac09e786d60212e
Reviewed-by: Eike Ziller <eike.ziller@digia.com>

src/plugins/coreplugin/mainwindow.cpp

@@ -30,6 +30,7 @@
 #include "mainwindow.h"
 #include "icore.h"
 #include "coreconstants.h"
+#include "jsexpander.h"
 #include "toolsettings.h"
 #include "mimetypesettings.h"
 #include "fancytabwidget.h"
@@ -119,6 +120,7 @@ MainWindow::MainWindow() :
     m_externalToolManager(0),
     m_progressManager(new ProgressManagerPrivate),
     m_variableManager(new VariableManager),
+    m_jsExpander(new JsExpander), // must be initialized after the VariableManager
     m_vcsManager(new VcsManager),
     m_statusBarManager(0),
     m_modeManager(0),
@@ -304,6 +306,8 @@ MainWindow::~MainWindow()
     m_helpManager = 0;
     delete m_variableManager;
     m_variableManager = 0;
+    delete m_jsExpander;
+    m_jsExpander = 0;
 }
 
 bool MainWindow::init(QString *errorMessage)